The way in which we define "life" has important implications for ethics, the definition of "animal" and even the range of creatures that can be credited with having minds. The definition which I am seeking here is both a conceptual one which does justice to our fundamental intuitions regarding life, and a theoretical one that attempts to describe just what it is that makes something alive. Beginning with Aristotle's "four-dimensional" account of life, I trace the history of philosophical thinking about the term "life" and locate the key positions taken on a "conceptual map". I argue that the recent invention of so-called "artificial life", which can be defined as an attempt to re-create the basic principles governing living systems, within a computational medium (Digital Life Lab at CalTech, 2002) has generated a philosophical crisis regarding the definition of "life". What were formerly thought to be the defining features of living things can be mimicked by abstract computational systems (Wolfram, 2002, pp. 824 - 825).
After reviewing the various definitions of "life" in the literature, I conclude that the teleological (end-directed) properties of life are basic and incapable of being reduced to lower-level properties. However, I also maintain that these properties supervene upon lower-level properties, allowing scientists to identify entities which are alive, according to strict empirical criteria. This does not entail reductionism, as the language we use to describe these properties cannot be divorced from teleology. I then attempt to construct a list of sufficient and necessary conditions for something's being alive, and address the question of why does the distinction between living and non-living matters ethically.
The question of whether the life versus non-life distinction is fundamental has bearings on my thesis for three reasons. First, how we answer this question could affect the way in which animals are defined, which is one of the aims of this thesis. If the answer is "no", then there is no a priori reason why we should exclude robotic animals (such as robotic bees, or AIBO, the robotic dog) from the scope of our definition of animals, which means that the domain of the animal kingdom may need to be enlarged.
Second, how we answer the question of what "life" is has profound implications for the nature of "mind". Thanks to recent advances in robotics, scientists are close to being able to construct robots whose behavioural feats equal or surpass those of many animals in sophistication - such as the InsBot robot, which is capable of infiltrating a group of cockroaches, influencing them and altering their behaviour (Pest Control Times, 16 November 2004, Web address http://www.pctonline.com/news/news.asp?ID=3071). This has important implications for the way we think about animal minds. The behavioural scientist J. S. Kennedy has argued that animals are really automata - an idea first considered and rejected by Aristotle, and adopted in more recent times by Gomez (1554) and Descartes. Although Kennedy takes pains to assure his readers that animals are not "simple machines ... making only fixed reflex responses to stimuli" (1992, p. 63, italics mine), he certainly regards animals as complex and unpredictable machines (1992, pp. 2-4). Even more recently, Wolfram (2002) taken the argument one step further, with his demonstration that even complex, unpredictable behaviour (including, he suggests, our own beheviour) can be generated by very simple algorithms.
The arguments put forward by Kennedy (1992) rely on a background assumption, which was first formulated as Morgan's Canon:
In no case may we interpret an action as the outcome of the exercise of a higher faculty, if it can be interpreted as the outcome of one which stands lower in the psychological scale (cited in Bavidge and Ground, 1994).Or as Kennedy puts it:
It might seem necessary to suppose that some animals have minds if we had no other explanation for their flexible, adaptive behaviour. But there is of course another explanation, namely the power of natural selection to optimize behaviour along with other features of organisms (1992, p. 121, italics mine).
For Kennedy, the error of mentalistic explanations of animal behaviour is that they confuse two kinds of explanations: proximate causal explanations, which answer the question of how behaviour occurs, and ultimate functional explanations, which explain its survival value (the ultimate "Why?"). Mentalistic explanations confuse these categories by making an ultimate cause appear proximate: the end of an action (its survival value) is seen as its subjective purpose, and hence its proximate cause. To say that an animal hunts because it experiences the subjective feeling of hunger is as anthropomorphic as saying that what makes a train go is "locomotive force" (1992, p. 51).
There is a good deal of popular support for the argument that if all of an animal's behavioural feats can be duplicated by a human-built robot or computer, then there is no need to impute a mind to the animal. Many people, upon hearing about some feat of animal cognition, are apt to object: "Yes, but even a computer could do that." But if there is some fundamental difference between robots and animals, then the whole analogy between them is undercut. In that case, the fact that a computer designed by human beings can do X mindlessly does not imply that an animal that can do X, does so mindlessly. (Indeed, one of my aims in this chapter is to show that there is some fundamental difference between living and non-living things: the former are bona fide individuals with a good of their own, while the latter are assemblages which lack intrinsic finality.)
If, on the other hand, it turns out that there is no fundamental difference between living and non-living things, then we have two choices in the debate on animal minds. We can choose to ascribe mental states only to those animals whose feats cannot be completely duplicated by a human-built computer - which in effect means that only humans, whose creativity enables them to stay one step ahead of their own computers by designing ever newer and better models, can be confidently credited with having minds - or we can "promote" artifacts and say that they have minds too.
There is a third reason why the question of whether there is any significant difference between living and non-living systems is a significant one: it alters the scope of our ethical concerns. If we allow that living animals are not fundamentally different from robotic ones, then depending on how we answer the question of whether animals have interests, we can choose to enlarge or restrict the scope of ethical concerns. If we allow that living animals have interests, then we have to consider the possibility that robots, too, may have interests, and even intrinsic value, as Davison (1999) proposes. Alternatively, if we find this idea ridiculous, then we may have to backtrack and entertain the notion that only people have interests.
Either choice has revolutionary implications. Practically everyone believes that we have a prima facie duty not to harm animals, but few people would consider it morally wrong to dismantle a Cray supercomputer that can defeat Garry Kasparov - or to pull the plug on a HAL-9000! Is this attitude a mere prejudice on our part - a case of bio-snobbery? Or are we, as J. S. Kennedy avers, guilty of anthropomorphism when we project some of our concerns onto animals?
It is not my intention to provide a detailed historical account of philosophical and scientific answers to the question of "What is Life?" in this thesis (but see Weber (2003) for a useful summary and critical evaluation of 20th century attempts to define "life"). Instead, what I propose to do is to situate some of the answers that have been given to this question, on a kind of "conceptual map".
Aristotle's account of life
Aristotle's four categories of causality - efficient, material, formal and final - provide a useful starting point for constructing such a conceptual map. Aristotle originally proposed these categories as an explanation of change: the efficient cause is that by which the change is brought about (i.e. the agent of change), the material cause is that in which the change is brought about (i.e. the subject of the change), the formal cause is that which is brought about (i.e. the transformation in the entity undergoing change), and the final cause is that for which the change is brought about, in those cases where the change is a goal-directed or purposeful one. Contemporary English usage of the term "cause" is much narrower than Aristotle's: today, the term is generally reserved for the first of his four causes.
Insofar as Aristotle taught that all four categories of causality were needed to answer the question, "What is it that makes (or causes) something to be alive?", his explanation of life can be characterised as four-dimensional. As Cameron (2000) convincingly demonstrates, there is overwhelming textual evidence that Aristotle regarded the four dimensions as mutually irreducible, and that he viewed final causality as a sui generis ontological category.
Aristotle criticised his materialist contemporaries, among them Democritus, for neglecting to include final and formal causality in their account of life, and for attempting to explain the phenomena of life using only two dimensions of causality - the material and efficient causes (Generation of Animals v.1 778b7-10; v.8 789b1-15).
The Scientific Revolution, commencing around 1600, also provided a two-dimensional, reductionist account of scientific explanation: every phenomenon in the universe was held to be explicable in terms of mechanical laws governing the motion and collision of particles of matter (Wilson, 1996; Wikipedia, 2004, arts. "Scientific Revolution", "Mechanism", "Vitalism").
Mechanism and Vitalism: Was Aristotle a Vitalist?
The philosophical debate about life from the 17th through to the early 20th century was dominated by a clash between mechanists and vitalists. Unfortunately, the philsophical discussion of this controversy is obscured by a lack of agreement in the literature (reviewed by Cameron, 2000, pp. 33-40) regarding the definition of the terms "mechanism" and "vitalism".
Aristotle has sometimes portrayed as a proto-vitalist. I would argue that this characterisation is erroneous, for two reasons. Firstly, Aristotle's four-dimensional account of life was much richer and far more sophisticated than the accounts that were subsequently advanced by scientists in either of the two "camps". Secondly, although Aristotle rejected reductionism, he regarded living things as continuous with the rest of nature. Overall, his views were closer to those of the mechanists than to the doctrines of the vitalists (Cameron, 2000).
One fact that emerges from Wilson's (1996) overview of the historical debate between mechanists and vitalists regarding "life" is that both camps argued within a two-dimensional framework. The key points at issue were: what kinds of laws applied to living things, and what sort of material they were made of. Mechanists asserted that the known laws of physics and chemistry, operating on ordinary matter in motion, could explain the phenomenon of life, while vitalists typically envisaged living things as being controlled by a "vital force" (elan vital) that obeyed special non-physicochemical laws and directed the continual generation of a unique class of organic compounds found within the bodies of living organisms. Indeed, vitalistic chemists (such as Berzelius) believed that these compounds could only be generated within living organisms, until other chemists succeeded in synthesising them via non-biological processes in the 19th century. These advances, coupled with experimental demonstrations that living things obeyed the laws of mechanics and thermodynamics, led to the eventual demise of vitalism as a scientific theory (Wilson, 1996). In short, the vitalistic explanation of life was quasi-mechanical from its inception, unlike Aristotle's four-dimensional account.
Additionally, there is no evidence that Aristotle thought living things violated physical laws, but there is abundant textual evidence (Cameron, 2000, pp. 41 ff.) that he regarded living things as materially continuous with non-living things - he believed in the spontaneous generation of life, for instance.
The philosophical discussion of mechanism and vitalism has been helpfully clarified by Cameron (2000), who distinguishes between strong and weak versions of both schools of thought (Table 1.1).
Table 1.1 - Strong and Weak Versions of Mechanism and Vitalism, as defined by Cameron (2000, pp. 36-39) (italics mine)
| Mechanism. Minimal definition: the belief that living things obey the laws of physics and chemistry. |
Vitalism. Minimal definition: the belief that the "aliveness" of an organism is completely independent of the interactions between its parts. |
| Strong mechanism: Organisms are nothing but chemical machines - all their properties and parts are wholly reductively identifiable with and explicable in terms of the laws of physics and chemistry as they apply outside of living systems. (Cameron has adapted this definition from Mayr, 1982.) | Strong vitalism: That property or entity in virtue of which living things are alive is: (i) irreducibly distinct from its physical properties and parts, (ii) to some extent determines the course of physical events in living things, and (iii) breaks or overrides physical laws in the course of (ii). |
| Weak mechanism: Organisms are 'something more' than chemical machines; although their activities do not conflict with the laws of physics and chemistry, at least some of their properties or parts are not wholly reductively identifiable with or explicable in terms of the laws of physics and chemistry as they apply outside of living systems (adapted from Mayr, 1982). | Weak vitalism: That property or entity in virtue of which living things are alive is (i) irreducibly distinct from its physical properties and parts, (ii) to some extent determines the course of physical events in living things, and (iii) fails to depend [i.e. does not depend - V.T.] for its existence on the interactions of such physical parts of living things as there may be. |
It should be noted that according to the broad definition proposed by Cameron, mechanism is not tied to a two-dimensional account of life. Indeed, Cameron (2000, p. 40) classifies Aristotle as a weak mechanist. (Wilson (1996), on the other hand, defines mechanism as a reductionist program for biology, which is why he classifies Aristotle as an organicist rather than a mechanist.)
Vitalism is no longer scientifically tenable: advances in the field of biology have decisively refuted even the weaker vitalistic claim that "living things somehow fail to depend on their physical parts for their being alive" (Cameron, 2000, p. 37). On the other hand, strong mechanism is regarded by modern scientists as too simplistic: contemporary mechanists "do not accept... that animals are 'nothing but' machines... The phenomena of life have a much broader scope than the relatively simple phenomena dealt with by physics and chemistry" (Mayr, 1982, p. 52).
That leaves us with weak mechanism. However, Cameron (2000, p. 35) faults Mayr's (1982) definition of weak mechanism for being too broad: as it stands, it is fully compatible even with Cartesian dualism, as a dualist need not maintain that non-physical minds violate the laws of physics and chemistry in their interactions with bodies. Since the prevailing scientific mind-set rejects all forms of dualism except some of the weaker varieties of property dualism, Cameron (2000, p. 38) has therefore defined a position - which he labels "sophisticated mechanism" - as a "precisification" of weak mechanism. Cameron characterises Aristotle's "emergentist" view of life as a via media between sophisticated mechanism and vitalism.
Table 1.2 - Sophisticated Materialism and Emergentism, as defined by Cameron (2000, pp. 36-39) (italics mine)
| Sophisticated mechanism: (i) living things are wholly composed of physical parts; (ii) some parts or properties of living things are not reductively identifiable with underlying physical parts and properties but are reductively explicable in those terms; and (iii) no property not reductively identifiable with underlying physical parts or properties has 'its own' causal powers; the causal powers of organisms are exhausted by the causal powers of their physical parts. |
Emergentist accounts: (i) living things are wholly composed of physical parts; (ii) all parts and properties of living things are causally or logically dependent for their existence on the interactions of their physical microparts; (iii) not every part or property of living things is a part or property fully reductively identifiable with the parts and relations of those same materials outside ofliving things; and (iv) the 'emergent' parts or properties noted in (iii) exert 'their own' causal influence over the course of their microparts' careers without breaking laws governing the behavior of microparts and properties. |
Table 1.3 - Aristotle's emergentist position compared and contrasted with sophisticated materialism and vitalism, according to Cameron (2000, pp. 36-40)
| School of thought | Sophisticated Mechanism | Aristotle's Emergentism | Weak Vitalism |
| Are there any activities in living things which violate physical laws? | No | No | No |
| Upward determination: Do higher level properties and parts of organisms depend for their existence on micro properties and parts? | Yes | Yes | No |
| Downward causation: do living things have higher-level properties whose causal powers are not exhausted by the causal powers of their underlying parts? | No | Yes | Yes |
Because Aristotle accepts upward determination, Cameron classifies him as a mechanist. According to Cameron, the crucial difference between Aristotle and contemporary mechanists is the issue of downward causation, which characterises Aristotle's emergentism (2000, p. 39).
The return of form
I would suggest that there are two important differences between 20th century scientific accounts of life and 19th century mechanist accounts: a revival of scientific interest in Aristotle's dimension of form, and the creation of a new, temporal dimension for explaining the phenomenon of life.
Hopkins' influential address to the British Association for the Advancement of Science in 1913, in which he set forth his vision of the emerging field of biochemistry, could be said to mark the renewal of scientific interest in form (Weber, 2003). What Hopkins proposed was a new model of the cell as a chemical machine, whose internal organisation was just as important as the chemical processes that regulated it.
The publication of Schroedinger's influential book "What is Life?" (1944) reflects a similar pre-occupation with form. Specifically, Schroedinger hypothesised that the molecular basis of life was an "aperiodic" solid with a "miniature code" embedded within its structure. His work had a powerful influence on Crick and Watson, the co-discoverers of DNA.
More recently, Davies (1999) has claimed that "[t]he secret of life lies, not in its chemical basis, but in the logical and informational rules it exploits" (1999, p. 212). Although his willingness to characterise life in terms of metabolism and reproduction makes him sound like a scientific mechanist, his recognition of the fact that both of these mundane processes require organisms to embody vast amounts of information clearly places him in the "formalist" camp.
Life's fifth dimension
Meanwhile, 19th century physicists investigating thermodynamics had developed a fifth dimension for explaining life: the temporal dimension. Whereas for Aristotle, "the phenomenon ... most basic in the apparent flux of the world was the unity and persistence of the individual living being" (Smith, 1976, p. 62, cited in Weber, 2003), modern scientists came to regard flux as a defining feature of life, as it responds to an ever-changing environment. Two recurring features of life - its order and its ability to evolve - attest to this fact in different ways.
According to the modern conception, the very stability of an organism is an indicator of its life-long active struggle against a hostile environment that is trying to break it down. Some physicists even attempted to define living things by their ability to continually generate order from disorder through their metabolism (Wolfram, 2002, p. 1178). Schroedinger's (1944) contribution to the debate was his proposal that living things achieved this task through the thermodynamics of open systems far from equilibrium.
Schroedinger's account of life can thus be seen as one which invokes the dimensions of form and the arrow of time to characterise living things in terms of both their structural and thermodynamic properties. The same could be said for Kauffman's (1993, 2000) recent proposal that a fourth law of thermodynamics might be needed to account for the self-organising properties of life.
The ability to evolve is such a pervasive feature of life that some neo-Darwinian biologists (e.g. Dawkins, 1976, 1986) are prepared to call anything that can evolve "alive". Their evolutionary paradigm of life relies heavily on the explanatory dimensions of form (i.e. DNA) and time (which produces variation through sexual recombination and mutation). Both evolutionary and thermodynamic accounts of life are inherently temporal, but there is an important difference between them: in evolutionary accounts, the changes envisaged are not those occurring within individual organisms during their life-long struggle against the forces of chaos (entropy), whereas in evolutionary accounts, slow, subtle inter-generational genetic alterations drive evolution, enabling some species to successfully adapt to changes occurring in their environment, over long periods of time.
The view I defend in this chapter is that it is possible to formulate a rigorous definition of life, but that we need five dimensions to do so: Aristotle's four causes, plus time. My neo-Aristotelian account of what it means to be alive explicitly invokes teleological causality, like that of Cameron (2000); unlike Cameron, I claim that there is nothing particularly mysterious about final causality, and that it supervenes upon Aristotle's other dimensions of causality - especially form - but is not reducible to these other dimensions. Lastly, I attempt to show that Aristotle's notion that each species of living organism possesses its own nature is fully compatible with Darwin's assertion that species change over time.
In this section, I argue that the quest for a definition of life has generated a full-blown philosophical crisis which has been largely ignored until very recently. "Crisis" is not a word I use lightly. The fact that all of the functional definitions that purported to list necessary and sufficient conditions for being alive have fallen foul of counter-examples does not constitute a crisis - after all, there are many things that cannot be defined in such a rigorous fashion. Not even the philosophical failure of the weaker cluster definitions of life that have replaced our old, simple definitions merits the term "crisis". Rather, what has caused the crisis is recent research with abstract computational systems, showing that even systems obeying very simple rules can instantiate properties once regarded as hallmarks of life (Wolfram, 2002). These systems are not generally considered alive or even life-like. To make matters worse, these simple systems can be found in nature too: indeed, they pervade the natural world. Commonly used definitions of life thus turn out to be full of holes, making ordinary distinctions between "animate" and "inanimate" appear to be nothing more than folk categories.
I argue that the root of all these problems is that the teleological aspect of life, which featured prominently in Aristotle's account, has been overlooked in most scientific definitions, and I discuss an Aristotelian definition of life proposed by Cameron (2000). The main obstacle to a widespread acceptance of teleological causation is that the metaphysics it rests on appears obscure and even "mystical". I put forward an explanation of teleological causation in terms which are amenable to contemporary scientific thinking, without reducing final causality to other philosophical categories.
1.3.1 Problems associated with the quest for single-attribute definitions of life
Traditionally, philosophers and scientists have approached the problem of defining "life" by looking for some distinguishing attribute or hallmark - for instance, some special capacity, function or mode of behaviour. However, "single-attribute" definitions like these are notoriously susceptible to three kinds of problems: counter-examples, borderline cases and category challenges.
Counter-examples
Functional definitions of life illustrate how vulnerable single-attribute definitions are to counter-examples. Attributes such as spontaneous self-movement or responsiveness to stimuli were once thought to be defining features of life, but as Descartes (1968, Discourse 5, pp. 73-74) realised, even machines with primitive sensors can duplicate these feats (see also Wolfram, 2002, p. 823).
The biological property of nutrition, which Wolfram defines as "the ability to take disorganized material and spontaneously organize it" (2002, p. 824) into its own structure, can be viewed as equivalent to a thermodynamic definition of life, insofar as the exercise of this function results in a local entropy decrease. But as Wolfram points out, "all sorts of systems - from crystals to flames - also do this" (2002, p. 824). Viruses, on the other hand, cannot not generate or store energy, but have to derive their energy, and all other metabolic functions, from the host cell.
Organisms tend toward homeostasis, an equilibrium of parameters that define their internal environment, but crystals can achieve equilibrium too (Cleland, 2002).
It is true that living things tend to reproduce themselves, but the attempt to define life in terms of reproduction generates well-known philosophical conundrums: is a mule alive? What about a fertile individual, who is unable to reproduce in the absence of a fertile individual of the opposite sex?
Additionally, as J.B.S. Haldane (1947, p. 56) pointed out, if we accept that life is essentially a pattern of chemical processes, it follows that any pattern that begets a pattern similar to itself - as a flame does, for instance - can be described as reproducing. (For Haldane, one thing that distinguished an organism from a flame was its additional capacity for self-regulation. However, "self-regulation" is a rather vague concept, and as we shall see below, it occurs in purely mechanical as well as living systems.)
It is certainly true that fires lack a mechanism of heredity, and do not evolve by natural selection (Maynard Smith, 2000). However, crystals in nature do instantiate a form of heredity: they may be perfectly aligned until a specific point is reached, in which a flaw has arisen. This flaw has a tendency to percolate down the subsequent layers of crystal, setting up a rudimentary system of heredity. Moreover, evolution by natural selection turns out to be a common feature of inanimate natural systems such as clay crystallites and autocatalytic networks of chemical species (Bedau, 1996, p. 338).
Of course, the fact that scientists have failed to find a single attribute that defines "life" does not mean that they cannot; it may simply mean (as I shall argue) that we need a better definition. But even if no definition could be found that was free of embarrassing counter-instances, the project of defining life would not have to be abandoned. One could still attempt to formulate looser definitions which listed properties that living things almost invariably possess and that inanimate objects generally lack. I discuss these cluster definitions below.
Borderline cases
It is commonly argued that borderline cases, such as viruses, evolving RNA strings in molecular genetics laboratories, frozen organisms and the exact point in time when the first true life-form appeared on the primordial earth (Bedau, 1996, p. 333; 1998, p. 132), render problematic any attempt to define necessary and sufficient conditions for life. Cameron (2000, pp. 30-32) responds to these criticisms by arguing that the demand for a clearcut definition is dogmatic and question-begging: it assumes that an adequate definition of X must provide us with an objective method for deciding, in all cases, if something is X. Imposing this kind of "decision procedure requirement" on all definitions imposes an improper epistemological constraint on natural categories such as "living things", which may not turn out to have sharp boundaries. Instead Cameron proposes a "no-epistemological baggage thesis" (2000, pp. 31-32), which states that an adequate definition of life "must tell us what conditions a thing must satisfy in order to be alive", but "need not yield objective decision procedures for determining in hard cases whether or not something is alive". The definition of "life" is thus compatible with a limited degree of ambiguity - a point recognised by Aristotle himself, who appears not to have regarded "being alive" as an "on-off" property (Cameron, pp. 40-42).
Category challenges
The project of defining hallmarks of living things has also come under fire from philosophers and scientists who question its implicit assumption that "life" is a property of individual organisms. Lovelock's Gaia hypothesis claims that the entire chemical and biological environment around the surface of the earth (including the oceans and the atmosphere) is alive. According to another bold proposal by Bedau (1996, p. 336), "life" is primarily a property of systems that are capable of "supple adaptation" - that is, "responding appropriately in an indefinite variety of ways to an unpredictable variety of contingencies". Individual organisms that make up such systems are said to be alive only in a derivative sense.
Cameron (2000, pp. 23-27) argues that while these new proposals may prove to be scientifically illuminating, they fail as definitions of life, insofar as they fail to satisfy a reasonable constraint which applies to all proper definitions - even to theoretical definitions which attempt to revise our concept of what something is. The constraint Cameron proposes is a categorial one: any proper definition of a concept must respect its fundamental ontological categories. The number 2 cannot be re-defined as a concrete material object; and neither can "life" be re-defined as a property of systems rather than individuals. If it should prove impossible to define life on the individual level, then it would be better to abandon the term "life" altogether.
However, the foregoing arguments do not appear to place the enterprise of defining life in serious danger. Even if we cannot find a single defining feature of life, cluster definitions might still do the trick.
1.3.2 Can cluster definitions work?
There is a widespread feeling among philosophers and biologists that the search for such a strict definition of life in terms of some single "hallmark" property, such as reproduction, is doomed to failure (Cameron, 2000, pp. 11-12). Many experts despair of being able to do anything more precise than writing down "a list of properties that we associate with life" (Farmer and Belin, 1992, p. 818). Bedau clarifies the thinking behind the cluster definitions of life proposed by these authors:
The individual properties in the cluster are held to be typically but not necessarily possessed by living entities; the diversity of living phenomena are thought to bear only a Wittgensteinian family resemblance (Bedau, 1996, p. 335).
Cluster definitions of life tend to fall into two groups - short and long - both of which have been subjected to criticism.
(a) Short cluster definitions
Table 1.4 - Properties listed in some recent short cluster definitions of life
| A potentially self-perpetuating open system of linked organic reactions, catalysed by stepwise and almost isothermally by complex and specific organic catalysts [enzymes] which are themselves produced by the system (J. Perret, 1952). |
| "Teleonomic" or purposeful behavior; autonomous morphogenesis; and reproductive invariance (Monod, 1971; cited in Bedau, 1996, p. 336). |
| Self-reproduction, genetics and evolution; and metabolization (Crick, 1981; cited in Bedau, 1996, p. 336). |
| Metabolism; self-reproduction; mutability (Kuppers, 1985; cited in Bedau, 1996, p. 336). |
| We regard as alive any population of entities which has the properties of multiplication, heredity and variation (J. Maynard Smith, 1975). |
| Metabolism; having parts with functions (J. Maynard Smith, 1986; cited in Bedau, 1996, p. 336). |
| Self-reproduction; and the capacity for open-ended evolution (Ray 1992; cited in Bedau, 1996, p. 336). |
The following definitions listed in the on-line "Life in the Universe" educational outreach program (organised by CERN, the ESA the ESO) were given by a panel of experts interviewed by Newton magazine (June 2001, Italian version) in a report entitled "Segnali di Vita Aliena" (Signs of Alien Life):
Haboku Nakamura - Biology Institute, Konan University, Kobe, Japan: Andre Brack - Centre for Molecular Biophysics of CNRS, France: Camilo J. Cela-Conde - Dept. of Philosophy, University of Baleares: |
Short cluster definitions of life are vulnerable to two flaws pertaining to the definition of any natural category.
First, although the above definitions share several common themes (reproduction, metabolism, heredity, variation, evolution and autocatalysis), the attributes cited lack unity, and give us no reason to think that the term "life" is a bona fide natural category:
A cluster offers no explanation of why that particular cluster of properties is a fundamental and ubiquitous natural phenomenon... (Bedau, 1996, p. 336).
Here, Bedau seems to be appealing to a general definitional requirement for any natural property, which I shall refer to as the unity-of-criteria condition:
Any adequate definition of a natural property P should explain the unity of the criteria for something's being P: what is it that makes all of them (and only them) criteria for being P?In this case, P refers to the natural property of being alive. An adequate definition of this property should explain why the assorted criteria listed, and no others, are criteria for life.
The foregoing cluster definitions fall foul of another definitional problem: they fail to account for what Cameron (2000) calls the problem of unity:
The problem of unity (PU): A condition of adequacy on an adequate definition of a property, P, is that it explain the unity of the items which fall into the extension of P: what is it that makes them all P? (2000, p. 50, italics mine).Here, Cameron presents his adequacy condition as one which applies to any property P. This is somewhat too sweeping - Wittgenstein's counter-example of the property of being a game comes to mind. However, the property of being alive purports to define membership of a natural category (unlike the category of all games). The unity of the objects belonging to a natural category is logically prior to any human declaration that they have something in common; for artificial categories, it is the other way round. Cameron's unity requirement is a reasonable one, provided it is restricted to any property P that defines membership of a natural category. It follows that any adequate definition of life should tell us why the term "life" applies to the range of things we call alive, and excludes inanimate objects.
Whereas the unity-of-criteria condition strives to unify the criteria for instantiating a natural property, Cameron's condition pertains to the unity of the entities instantiating it. The above cluster definitions of life fail to satisfy either requirement.
A final problem with short cluster definitions is their vulnerability to robust counter-examples. For instance, physicists have recently created cell-like blobs of gaseous plasma which, despite their lack of a mechanism for heredity, satisfy the four main criteria generally used to define living cells: they possess a boundary layer that separates their interiors from the external environment; they can replicate by splitting in two; they can grow by taking in atoms and splitting them into ions and electrons to replenish their boundary layers, and they can communicate information by emitting electromagenetic energy that causes neighbouring "cells" to resonate (Cohen, 2003). However, nobody would think of describing these gaseous blobs as "alive". It seems that a more complete description of life is needed.
(b) Long cluster definitions
Because they are comprehensive, long cluster definitions are much less vulnerable to the counter-examples cited above. Long definitions have the additional merit of deepening our understanding of "life". A representative sample of such definitions is listed in the table below.
Table 1.5 - Properties listed in some recent long cluster definitions of life
|
1. All levels of living systems have an enormously complex and adaptive organization.
2. Living organisms are composed of a chemically unique set of macromolecules.
3. The important phenomena in living systems are predominantly qualitative, not quantitative.
4. All levels of living systems consist of highly variable groups of unique individuals.
5. All organisms possess historically evolved genetic programs which enable them to engage in 'teleonomic' processes and activities. [See below for definition of 'teleonomic'. - V.T.]
6. Classes of living organisms are defined by historical connections of common descent.
7. Organisms are the product of natural selection. 8. Biological processes are especially unpredictable (Mayr, 1982; cited in Bedau, 1996, p. 336). Note
The term "teleonomy" is defined by Maturana and Varela (1979) as follows: the element of apparent purpose or possession of a project in the organization of living systems, without implying any vitalistic connotations. Frequently considered as a necessary if not sufficient defining feature of the living organization.
|
|
Self-reproduction; information storage of self-representation; metabolization; functional interactions with the environment; interdependence of parts; stability under perturbations; and the ability to evolve (Farmer and Belin, 1992, p. 818; cited in Bedau, 1996, p. 335).
|
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Life is a succession of energy-producing electro-chemical processes
by a naturally occurring, simple or complex organism composed of a combination of molecules,
forming cells, which consume 'food' and produce 'waste', both consisting of solid, aqueous, and gaseous matter;
the process is called metabolism;
the organism is capable of living within the environment without dependency on any other organism;
energy use is manifest by growth with size limits for most;
self-healing;
possibly movement;
self-replication with each offspring slightly different;
irritability;
capable of modifying their living environment, both beneficially and detrimentally;
with eventual termination of energy production, or death.
Exceptions are egg, sperm, spore, seeds and virus, which do not consume food or produce waste; the first four are replication structures, and the fifth has premature life-terminating capabilities.
(Definition proposed at a 1993 symposium entitled "What is Life? Define Life", organised by C. Gordon Winder at the biennial International Society of History, Philosophy, Social Studies of Biology (ISHPSSB) conference at Brandeis University, Waltham, Massachusetts.
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Sidney Fox - South Alabama University, USA:
Living beings are protein-made bodies formed by one or more cells that communicate with the environment through information transfer carried out by electric impulses or chemical substances, and capable of morphological evolution and metabolism, growth and reproduction. The above definition by Sidney Fox of South Alabama University, USA, is listed in the on-line "Life in the Universe" educational outreach program (organised by CERN, the ESA the ESO). Fox was one of a group of experts interviewed by Newton magazine (June 2001, Italian version) in a report entitled "Segnali di Vita Aliena" (Signs of Alien Life).
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Shane Sarver (1999), Associate Professor of Biology at Black Hills State University, South Dakota, lists the following seven features of living things on his Web page "Definition of Life and Intro. to Zoology": (1) chemical uniqueness (living things contain large complex macromolecules, made up of the same building blocks - nucleic acids such as DNA and RNA, proteins, lipids and carbohydrates);
(2) hierarchical organisation (molecules are nested into cells, the building blocks of all living systems, which are nested into tissues, tissues into organs, and organs into an organism);
(3) reproduction, which enables the transmission of traits from parents to offspring;
(4) a genetic program, or script (usually contained in DNA), that codes for the make-up of living things;
(5) metabolism (extraction of chemical energy from nutrients);
(6) the occurrence of characteristic phases of development in a life cycle; and
(7) interaction with the environment: ecology is the study of this interaction. (N.B. The definition of life on Sarver's (1999) Web page is also used by other universities. It can be accessed from the University of Toronto Zoology department home page by clicking on the link "Careers in Zoology", which takes you to the Web page, "What is Zoology?". This page has a link, "Definition of Life", to Sarver's Web page.)
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Former "Science" editor-in-chief Daniel Koshland (2002) lists seven "pillars of life":
(1) a program, i.e. "an organized plan that describes both the ingredients themselves and the kinetics of the interactions among ingredients as the living system persists through time" (Koshland, 2002, p. 2215);
(2) improvisation, or a way of changing its master program (achieved on Earth through mutation);
(3) compartmentalisation (a surface membrane or skin, and for large organisms, a subdivision into cells, in order to preserve the ingredients required for chemical reactions at their required concentrations);
(4) energy (which on Earth comes from the Sun or the Earth's internal heat), to keep living systems metabolising;
(5) regeneration (this includes reproduction), to compensate for the wear and tear on a living system;
(6) behavioural adaptability to environmental hazards; and (7) seclusion, or some way of preventing one set of chemical reactions from interfering with another, in a cell. |
One could fault most of these definitions for their inclusion of properties that are either too ad hoc (why should the presence of DNA, proteins or even carbon figure in our definition of "life"?) or too vague and uninformative (e.g. "information storage" or "interaction with the environment"). Another pertinent criticism of these criticisms is that as Cleland and Chyba (2002) argue, a laundry list is a dangerous way to define natural categories. The two authors cite the example of water: one could attempt to define "water" as anything that is wet, odorless, tasteless, and thirst-quenching, but even this definition "could still allow substances that superficially resemble water to be incorrectly classified as water".
Perhaps the greatest failing of these definitions is that they only serve to exacerbate the philosophical problems with regard to the definition of life, which they were meant to resolve. Bedau's comment on Mayr's "especially comprehensive" cluster definition is illuminating:
Mayr's list ... cannot help but deepen our sense of wonder and perplexity about what root cause could conspire to make this striking collection of features present in such an indefinite diversity of natural phenomena. We want an account of why these properties all coexist. Rather than settling this question, the list raises it (Bedau, 1996, p. 336, italics mine).
It is readily apparent that long cluster definitions of life, like short ones, fail to satisfy the unity-of-criteria condition or to solve Cameron's problem-of-unity (2000, p. 50).
Bedau concludes that "[a] cluster conception is a fall-back position that can be justified only after all candidate unified views [of life] have failed" (1996, p. 336).
Despite these failings, the long cluster definitions listed above are not without merit, as they embody some rich philosophical insights, which I intend to make use of below when putting forward my own neo-Aristotelian account of life. I also argue that some of these definitions, rightly interpreted, contain empirical criteria that enable us to distinguish living from non-living things.
1.3.3 Is it too soon to formulate a good definition?
In the face of the above criticisms, many scientists, whom I shall refer to as "inopportunists", regard the question of life's definition as unanswerable for the time being. One commonly cited reason for this pessimism is that all the life-forms we are familiar with are terrestrial and share a common origin (Cleland, 2002). Despite its apparent diversity, it is claimed, life on Earth is really only a single case. While I am prepared to grant for the sake of argument that all life on Earth is monophyletic, I do not regard this line of argumentation as particularly convincing. Terrestrial bias would certainly be a relevant factor if we were trying to identify the chemicals necessary for life, but the problem with defining life lies elsewhere. "Life" is not a purely chemical category: if it were, there could be no debate about whether so-called "artificial life-forms" such as computer viruses are truly alive. In ordinary usage, the term "life" is usually taken to designate some kind of activity or process.
Another argument against constructing preliminary definitions of life is that as yet, we lack a general "theory of life". Cleland and Chyba (2002) remark that medieval alchemists classified many kinds of substances as "water", including nitric acid (which was called aqua fortis). Only with the advent of molecular theory were scientists able to understand why nitric acid, despite sharing many of the properties of water, is nonetheless not water. But as McKay (2004) remarks, the analogy of life with water is not a particularly good one: the term "water" designates a material, whereas "life" refers to some kind of process. In any case, the chemical processes that take place in living cells are well-understood.
One could argue that even if we understand the chemistry of life, we do not yet understand how blind chemical processes could have given rise to the vast quantity of information that must have been embodied even in the first living cell, in order for it to be able to reproduce and metabolise (Davies, 1999). While I have no quarrel with Davies' suggestion that an understanding of how life started may shed light on what it is, I would like to point out that the latter question is logically independent of the former. Generally, we do not have to know how X's originate in order to grasp what they are.
I conclude that the "inopportunists" have failed to make a good case against pressing ahead with the attempt to define life.
1.3.4 The new crisis regarding the definition of life
Although the ad hoc cluster definitions of life we examined above proved to be philosophically unsatisfying, they are hardly a cause for panic. Cluster definitions, after all, possess the virtue of rendering the definitional problems caused by awkward borderline cases more manageable, while keeping the phenomenon of life reasonably well-delineated.
Recently, however, Stephen Wolfram (2002) has argued that no "general definition of life, independent of the details of life on earth ... can actually be given", because "almost any general feature that one might think of as characterizing life will actually occur, even in many systems with very simple rules" (2002, p. 825, italics mine). The originality of Wolfram's contribution consists not in his assertion that all of the alleged distinguishing characteristics of life are shared by some inanimate objects, but that a very large class of simple systems - which nobody would even think of calling alive - share these characteristics. The definitions of life turn out to be as full of holes as a leaky sieve: they are not even approximately correct. This situation, I would argue, merits the term "philosophical crisis".
Metabolism, or "the ability to take disorganized material and spontaneously organize it" (Wolfram, 2002, p. 824) is a common feature of cluster definitions of life. But as Wolfram shows, "self-organization is actually extremely common even among systems with simple rules", including "all sorts of systems" in nature (2002, p. 824).
The property of self-reproduction fares no better:
[I]n the 1950s abstract computational systems were constructed that also had this ability. Yet it seemed that they needed highly complex rules - not unlike those found in simple cells. But in fact ... even systems ... with remarkably simply rules can still manage to show self-reproduction (2002, p. 824, italics mine).
Evolution by natural selection likewise turns out to be a common feature not only of inanimate natural systems (Bedau, 1996, p. 338), but also of man-made computational systems. Recently, Lenski et al. (2003) have created digital organisms - simple computer programs that self-replicate, mutate, compete and "evolve" solutions to complex problems in a Darwinian, step-wise fashion, demonstrating that "complex functions can originate by random mutation and natural selection" (Lenski et al., 2003, p. 139; see also Knight, 2003). Should we think of even these simple programs as "alive"?
Additionally, Wolfram's work on computational irreducibility (2002, pp. 737-750) demonstrates that unpredictable behaviour is a common feature of the inanimate world. For all except the very simplest sytems that are found in nature, there are no predictive short-cuts: even with a complete knowledge of the rules and initial conditions of a system, it can still take an irreducible amount of computer work to calculate its future behaviour, which means that "in effect there can be no way to predict how the system will behave except by going through almost as many steps of computation as the evolution of the system itself" (2002, p. 739).
Even the much-vaunted complexity of life is dismissed by Wolfram, on the grounds that a vast range of systems, even "ones with very simple underlying rules ... can generate at least as much complexity as we see in the components of typical living systems" (2002, pp. 824-825). This claim is elaborated in Wolfram's Principle of Computational Equivalence. In a nutshell, it says that (i) almost all systems, except those whose behaviour is not "obviously simple", can be used to perform computations of equivalent sophistication to those of a Turing mechine, and (ii) it is impossible to construct a system that can carry out more sophisticated computations than a Turing machine (2002, pp. 720 - 721; the latter part of the Principle is also known as Church's Thesis).
Wolfram suggests that the reason why we can easily distinguish living from non-living systems in everyday life is that living things share a lot of specific structural and chemical features - such as "being made of gelatinous materials and having components [like] proteins, enzymes, cell membranes and so on - and ... being based on specific chemical substances ... water, sugars, ATP and DNA" - reflecting "their long history of biological evolution" (2002, p. 825). Untutored laypeople may not grasp chemical concepts (such as "gelatinous material") at the micro-level, but they can certainly recognise chemical properties at the macro-level. We all know a bone when we see one. Hence our ability to recognise members of the folk category "life".
But if chemistry alone is what makes something alive, then one has to query the scientific and ethical relevance of the term "life".
Incidentally, Wolfram's Principle of Computational Equivalence has a very important philosophical consequence for the debate about how living things differ from computers. What it means is that we can no longer classify living things in a separate category from computers: living things - bacteria, plants and animals (including human beings)- are computers, insofar as their bodies can be used to perform the kinds of computations that a Turing machine can perform. The question of whether some computers qualify as living things presupposes that computers are a subset of the set of living systems, whereas in fact, the reverse is the case. Philosophically, it would be more appropriate question to ask whether there is a significant difference between artificial computational devices and living organisms.
1.3.5 What is wrong with the foregoing definitions of life?
I suggest that there are two major problems associated with the above definitions of life, and I propose to characterise these problems in terms of the five "dimensions" of life which I highlighted earlier (Aristotle's four causes plus time). The two problems are a general (though by no means universal) failure of scientists to adequately characterise the formal features of living things, coupled with an almost complete neglect of the teleological aspect of life.
The formal features of life identified in the preceding definitions are deficient on various counts. Some of the formal attributes listed were arbitrarily specific, focusing on particular structures such as the DNA molecule. Yet even if it turned out that all life was DNA-based, we would still need to know what made DNA special.
Other accounts were too vague, attempting to characterise life in terms of general features that can be readily found even in the inanimate world (such as complexity, or a self-replicating pattern of chemical processes), or which establish only a quantitative difference between living and non-living things (such as information content).
Some accounts (Monod, 1971; Winder, 1993; Sarver, 1999) contained references to the distinctive morphological features of living things - such as cells, tissues and organs. However, the instructions needed to assemble the structures that make up the body of a living creature are contained in its genetic program. This suggests that the program that directs the make-up of these structures should be considered the central formal feature of living organisms.
A few of the long cluster definitions (Mayr, 1982; Sarver, 1999; Koshland, 2002) actually highlighted the existence of a genetic program that codes for the make-up of living things. But "programs" alone cannot suffice to define living things: programs (defined broadly as rules that govern the behaviour of an entity) are ubiquitous in nature (the laws of physics are a well-known instance), as well as in abstract computational systems (Wolfram, 2002, p. 383). What makes the programs in living things fundamentally different from other programs? Any satisfactory account of the form of an organism has to answer this question.
Our provisional conclusion is that the prospects of being able to define life in terms of some combination of efficient causality (which features prominently in functional definitions of life), matter (invoked in chemical as well as functional definitions), form (which figures in many long cluster definitions) and time (thermodynamic and evolutionary definitions) appear to be remote. These factors alone do not suffice to determine that something is alive: as Wolfram (2002) has shown, most of the features instantiating these dimensions are actually very common in nature.
Aristotle's dimension of final causality has been curiously neglected in most of the contemporary definitions of life given above, with a few notable exceptions: Mayr's (1982) fifth condition refers to teleonomic processes and activities in organisms (made possible by their genetic program), Monod's (1971) definition also refers to "teleonomic" or purposeful behaviour; Maynard Smith (1986) makes having parts with functions a defining feature of life; and Sarver's (1999) second condition - hierarchical organisation - suggests some kind of teleological organisation. It would be tempting to invoke this much-neglected dimension as the solution to our definitional problems regarding "life", but before we can do so, we need to address the reasons why many philosophers and scientists have chosen to set aside finalistic (teleological) accounts of life.
1.3.6 Is teleology redundant?
Final causation is out of favour in modern scientific circles, as it is incompatible with a "scientific world-view that countenances only efficient causation" (Buller, 1999, p. 6, italics mine). Accordingly, those who wish to do away with teleological talk in science have two choices: eliminate the very concept of teleology, or reduce it to something more scientifically respectable.
Eliminativism, as we shall see below, is not a viable option. Teleology is real. Proponents of final causation, such as Cameron (2000, 2004), have therefore focused their attack on reductionism, arguing that attempts to reduce teleological properties to structural properties or historical properties fail to account for their goal-directedness and biological normativity.
My own intermediate position, which I shall elaborate in section 1.4, is that (i) the structural and/or historical properties of some part of an organism can indeed determine whether it is goal-directed and subject to biological norms, but (ii) it is impossible in principle to describe the formal and historical properties of these parts without employing some teleological language, hence (iii) the attempt to reduce teleology to some other explanatory "dimension" of life is doomed to failure. On point (i), I part company with Cameron. In this section, I shall limit myself to briefly cataloguing the formidable (and as yet unsolved) philosophical problems that any reductionist program needs to address. (Cameron (2000, pp. 168-213) contains a very comprehensive discussion of these problems.)
The failure of eliminativism
The "eliminativist" option appears unworkable: as biologist Karen Neander points out, "the apparent explanatory power of teleological explanations which appeal to biological functions is quite robust" (1991, p. 127). (Cameron (2000, pp. 171, 219-220) lists citations from several other scientists who uphold the relevance of teleological explanations.) Neander calls teleology the "conceptual glue" of biology and notes that it would be "hard to exaggerate" the concept's importance to biology (1995, p. 227).
Walrus tusks provide a good illustration of this point. The question of what they are for is surely a meaningful one, and it is certainly legitimate, from a scientific standpoint, to investigate the many functions they serve (for fighting, especially during the mating season; for protection against predators; as anchors, when hauling their bodies out of the water; as pickaxes to cut a path through the ice; and for anchoring themselves on the ocean bottom while digging for clams).
The inadequacy of eliminativism leaves us with the option of assimilating teleology to something else - in other words, "to analyze the concepts of being a goal and being goal-directed so that the analytic versions of these concepts ... contain no undefined teleological notions" (Nagel, 1979, p. 291). The two most popular proposals for realising this project are the systems approach to teleology and the etiological account of functions, both of which are critically surveyed by Cameron (2000, pp. 174-213; 2004).
The systems approach to teleology
The systems approach endeavours to explain teleology as a structural feature of certain complex systems. A well-known problem with this approach is that the same structural features can be found in systems which nobody would describe as teleological. Bedau (1992) argues that even if we make these features more robust, non-teleological counter-examples with the same structural features can still be found. In other words, "a system's [intrinsic] causal dynamics do not by themselves determine whether the system is genuinely goal-directed" (Bedau, 1992, p. 265).
It is, of course, possible that living things do in fact have unique structural features, which have not yet been properly described or enumerated by scientists. I shall return to this point in section 1.4.1. However, I would like to point out that even if (as I suggest below) the structural features of a system can determine whether it is goal-directed, that does not establish the success of the reductionist program. In order for the program to succeed, it needs to be shown that these structural features can be described without any reference to their goal-directed properties. I shall argue below that it is precisely at this point that the reductionist program falters.
The etiological account of functions
Most contemporary scientists attempt to account for the occurrence of biological functions, in terms of an etiological account. The key idea here is that items with proper functions must have a history of selection. An item's past history (which made it biologically advantageous) explains its present use: "the proper function of a trait is to do whatever it was selected for" (Neander, 1991, p. 124). For instance, "grasping objects was what ... the opposable thumb was selected for, and that is why it is the function of your thumb to help you grasp objects" (Neander 1991b, p. 130).
Varner (1998) provides a clear, attractive summary of the etiological account, based on the work of other authors in the field:
X is a biological function of S (some organ or subsystem) in O (some organism) if and only if:(a) X is a consequence of O's having S and(b) O has S because achieving X was adaptive for O's ancestors (1998, p. 67).
In appealing to history and natural selection to explain teleology, the etiological account draws upon two of the five "dimensions" I described in section 1.2 - the temporal and efficient causal "dimensions". The etiological account can therefore be considered as a reductionist explanation of teleology.
One advantage of explaining functions on an etiological account is that it can easily explain the functionality of an organ in awkward cases where the creature possessing it is unable for accidental reasons (e.g. injury or sterility) to benefit from it. Thus even if an animal is blind or unable to reproduce, its eyes can be said to possess a function such as sight, because its ancestors enjoyed a selective advantage by being able to see. However, a straightforward non-etiological explanation is also possible: the animal's eyes can be said to possess a function because eyes in other (healthy) members of its species have a function.
If the etiological account is right, the teleological language we use when talking about living things can be grounded in their history of natural selection. However, there are formidable problems with the etiological account, which are described in detail by Cameron (2000, pp. 176-213).
First, the etiological account undermines the authority of biologists whose specialty is not evolution (e.g. physiologists) to attribute biological functions to organs, without reference to their evolutionary past. We accept the statement that the heart's function is to pump blood, simply because physiology tell us so; but if the etiological account is correct, any attribution of function made by a physiologist is in principle revisable, if contrary evidence from evolutionary history comes to light.
The fact that it is possible for scientists to deduce the functionality of an organ or biological subsystem in a living creature, without looking at its ancestors, is a major stumbling block for the etiological account. As Richard Dawkins puts it:
[A]ny engineer can recognize an object that has been designed, even poorly designed, for a purpose, and he can usually work out what that purpose is just by looking at the structure of the object (1986, p. 21, italics mine).
It is certainly true that scientists do sometimes talk about the original function of a structure that presently has none (e.g. vestigial legs in snakes) and that they also distinguish between the original function and the present function of an organ or biological subsystem. For instance, the opiates in an animal's body not only have the biological function of pain relief, but also of attacking bacteria and sending signals to the immune system, which appears to have been their original function (Stefano, Salzet and Fricchione, 1998). In these cases, the etiological account performs a valuable service of rendering intelligible our attribution of original functions to biological structures. But even here, the attribution of an original function is made by comparing the structure or subsystem with equivalents in present-day organisms, as the organs of ancestral forms are seldom preserved. This is precisely what Stefano, Salzet and Fricchione (1998) did: they examined the biochemistry of living invertebrates.
A second problem with the etiological account is that it flouts what appears to be a reasonable categorial constraint on proper theoretical definitions of concepts: namely, that a proper definition of an existing concept should not attempt to place it in a new ontological category. We cannot re-define the number 2 as a color, because category constraints prevent us from doing so. Likewise, it is philosophically illegitimate to attempt to re-define functions as historical properties.
This point is borne out by counter-examples which appear to show that a history of natural selection is neither necessary nor sufficient for the possession of a biological function. It is not necessary, because we can conceive of cases where we would still confidently ascribe functions to a creature's organs, even if they had no evolutionary history: if an instant lion appeared in our midst, we would have no hesitation in saying that the function of its heart was to pump blood. Nor is it sufficient: there are actual cases of entities (clay crystallites) possessing complex structures that undergo a process of natural selection (Cameron, 2000, p. 205). No-one has suggested that these inorganic entities are alive, and in any case, their parts appear to have no function: they are not for the sake of anything.
Although Cameron's real-life counter-examples to the notion that an organ's having history of natural selection is sufficient for its possessing a natural function are persuasive, his argument against the necessity of a history of natural selection is that it relies heavily on thought experiments relating to situations which, while logically possible, may or may not be really possible. In the Introduction to my thesis, I cautioned against reliance upon arguments of this kind.
Fortunately, there are better cases at hand. Varner (1998, p. 67) himself acknowledges that his definition of "biological function" fails to confer functionality on the first organism to possess an adaptive mutation, such as a photosensitive spot, or "proto-eye" - a difficulty to which Varner responds by suggesting that new traits acquire biological functions only via subsequent selective pressure, which presumably means that the first organism on earth had no functions!
Artificial selection poses an even weightier problem. For it is by no means clear why a function that arose through artificial rather than natural selection should not be considered biological. For instance, there are some species of eyeless fish whose ancestors possessed a sense of sight but who have since lost it because they live in underwater caves where having eyes is actually a biological disadvantage, as the eyes are liable to bacterial infection if injured from the fish's occasional collisions with cave walls. The DNA in these fish still contains the genetic program for constructing eyes, but it has been switched off. If future scientists succeeded in switching on this eye-making program, and released a group of genetically engineered fish into an environment where sight was an advantage, we would surely say that the function of their descendants' eyes was to see, even though their ability to do so was the product of artificial rather than natural selection.
Despite these troubling exceptions, we should not overlook the fact that the etiological account encapsulates a powerful insight: that all present-day functions of organs or biological subsystems in living things arose because they were advantageous to their ancestors. The etiological account is therefore universal in scope, if we leave aside genetically engineered organisms.
A final problem with the etiological account, according to Cameron, is that it is incapable of generating biological norms, and explaining how organs can malfunction, or fail to do what they are supposed to do. The fact that a part is adapted and selected by Nature for doing something does not endow the part with a biological function, any more than my artificial selection of a trait in a lineage of laboratory organisms would give that trait a function:
There is neither purpose nor function to natural selection, nor resulting from natural (or artificial) selection. What is selected is simply selected, and what the selected does it merely does (2004, p. 5).
I am not persuaded by Cameron's argument on this point. There is an important difference between natural and artificial selection: in the former case, the trait is selected because its properties make it intrinsically advantageous in the organism's biological habitat; whereas in the latter case, the trait is selected for non-biological reasons. In the natural case, there is a real sense in which the trait per se promotes the organism's survival, given its biological environment: the trait itself explains the selective advantage of organisms possessing it. This warrants our making the biologically normative statements that (i) organisms of the same species, living in the kind of environment where the trait confers a selective advantage, should have the trait; (ii) the trait has the function of doing whatever it does to improve the organism's chances of survival.
Cameron also argues that the fact that an organ has worked in the past does not generate any biological norms about how it should work now or in the future. But if an organ "works" over a period of millions of years (under a certain range of environmental conditions), then it is sensible to assume that there is some law of nature that explains why it works. If there is such a law, then our reliance on it to hold in the future (under the same range of conditions) is no more problematic than our reliance on any other law - e.g. gravity. The biologically normative content of the law reflects the underlying notion that biological norms are simply those kinds of behaviour that inherently tend to promote an organism's survival.
However, even if etiology can generate biological norms, a number of outstanding problem cases remain. As Cameron (2004) points out, etiology per se is neither necessary nor sufficient to yield such biological norms: an instant lion's heart - or, if we employ my less controversial example, the eye of a genetically modified cave fish - could malfunction, and there is nothing that clay crystallites are supposed to do, despite their history of selection.
Thus far, we have focused on the philosophical inadequacies of the etiological account of functions. However, even if the foregoing problems could be resolved, I contend that there is a more fundamental problem with the etiological account: it fails to reduce teleology to the dimensions of time and efficient causality, as it set out to do.
It is important to distinguish here between the following questions that can be legitimately asked regarding any biological organ or subsystem S:
1. How did S arise?2. How did S become prevalent?
3. Why did S become prevalent?
4. Why does S persist?
5. What is S for?
The Darwinian answer to the first question is: random variation. (Hence the question: "Why did S arise?" is meaningless.) The etiological account claims to provide an answer to the remaining four questions, reducing the fourth and fifth questions to the third. What I would like to point out here is that even the third question cannot be answered without reference to (a) the organism as a whole, and (b) advantages enjoyed by previously existing organisms subsequent to the acquisition of the trait. I shall employ the example of the opposable thumb to illustrate my point.
1. How did the opposable thumb arise? (Answer: by a process of random mutation.)
2. How did the opposable thumb become prevalent? (Answer: it conferred a selective advantage on individuals possessing it.)
3. Why did the opposable thumb become prevalent? (Answer: because individuals born with this trait were subsequently able to grasp objects once they became old enough to fend for themselves, giving them a selective advantage.)
4. Why does the opposable thumb persist? (Answer: because individuals born with this trait are able to grasp objects once they are mature enough to fend for themselves, giving them a selective advantage.)
5. What is the opposable thumb for? (Answer: it is for grasping objects.)
Of the four questions which the etiological account claims to answer, only question 2 is purely historical: any existing organ or subsystem with a biological function became prevalent in the general population because its possessors lived longer and left more descendants than their rivals. However, question 2 cannot tell us what the function of the relevant organ or subsystem is; all it tells us is that the organ or subsystem must have some function, as it is biologically advantageous. To discover what the function is, we need to answer question 3, at the very least.
But even if we reduce questions 4 and 5 to question 3, we cannot dispense with the holistic reference to the organism, nor can we avoid referring to "future" states or abilities of the organism, subsequent to the acquisition of the adaptive trait (e.g. its ability to grasp objects when it is old enough to fend for itself). To explain why the trait is present, we have to "look ahead".
I conclude that etiology, despite its promising insights, is incapable of reducing the teleological aspect of biological functions to a more scientifically "respectable" combination of efficient causation and history.
Can etiology be used to explain what it means to be alive?
According to Varner's (1998) bold proposal, an etiological account of functions not only explains functionality, but can also be used to explain what it means for an organism to be alive.
Varner makes a sharp distinction between biological functions and an organism's built-in goals, or end-states. What is good for an organism cannot be adequately defined in terms of its end-states, as artifacts - such as a Patriot missile - may also have "built-in goals". (I shall revisit Varner's example of the missile in section 1.4.5.) Instead, Varner proposes that "biological functions, rather than goals or end-states" are required to "draw a sharp distinction between all artifacts, on the other hand, and all living organisms on the other" (1998, p. 67).
According to Varner, the crucial difference between organisms and artifacts is that organisms evolve:
One thing that distinguishes organisms from artifacts is that the former but not the latter are the result of natural selection (1998, p. 69).
Because all living things evolve, it is appropriate to ascribe biological functions to their organs or subsystems (e.g. the function of eyes is to enable their possessor to see). Artifacts do not possess functions; they merely have needs. Varner thus distinguishes life from non-life in terms of functionality, rather than finality - exactly the opposite of the position that I am arguing for.
However, Varner's claim that artifacts lack built-in functionality is empirically false, as it rests on the assumption that natural selection is a feature of natural systems only. As we have already seen, natural selection can occur in abstract computational systems too (Lenski, 2003). Additionally, one can envisage concrete, physical artifacts which undergo natural selection - for instance, a von Neumann probe, described in a thought experiment by the physicist Frank Tipler (1982). As Tipler conceived it, such a probe would travel around the Galaxy, guided by an in-built computer "capable of self-replication and capable ... of constructing anything for which it has plans, using the raw materials available in the solar system it is aimed at" (1982, p. 34). If the von Neumann probe also had a modifiable program, which occasionally (when the program mutated) acquired new functionalities that help them to make more replicants of themselves, then these functionalities would be subject to natural selection in their different planetary environments.
Varner's proposal that we can account for the distinction between life and non-life in etiological terms thus appears to be at odds with the available evidence.
I conclude that teleology remains an irreducible, ontologically primitive fact of life.
1.3.7 Are there any good methodological reasons for rejecting teleological accounts of life?
Despite the problems facing non-teleological accounts of life, there are many philosophers and scientists who reject teleological explanations for purely methodological reasons. Cameron (2000) addresses some common reasons for excluding final causality from scientific explanations, refuting oft-repeated assertions that teleology implies a pre-existing commitment to animism, or panpsychism, or the existence of God, or the benevolence of nature, or a belief in "progressive" evolution, or vitalism (2000, pp. 215-219). In fact, teleology is compatible with the rejection of any or all of these beliefs. A related worry is that belief in teleology commits one to backward causation, but this objection seems to mistakenly presuppose that teleological causation is simply efficient causation running backwards in time, when in fact, final causality is not the same as efficient causation of any sort (2000, p. 218). Backward causation, as understood by Aristotle, simply means that some biological processes occur for the sake of future benefits to the organism. I discuss downward and backward causation at further length in section 1.4.4.
It is frequently objected that teleological explanations are vacuous, but Cameron (2000, pp. 219-220) argues that they are no more vacuous than explanations invoking efficient causation. The idea of something's being directed towards an end may seem obscure, but the notion of something's possessing a causal power to bring about a certain result is surely equally mysterious. If teleology is an irreducible part of the natural world, he argues, we should put aside our metaphysical prejudices and accept it.
1.3.8 Is a teleological account of life intelligible?
More specifically, Cameron (2000, pp. 240-279) proposes that teleology is a strongly emergent property of organisms, in the sense that although it depends causally for its existence on the interactions between their parts, it is irreducibly distinct in kind from the properties of these parts, and possesses causal powers not possessed by the parts and their interactions.
Emergence may seem a strange, almost magical notion to some, but Cameron contends that if we accept Hume's argument that "we are in a natural state of ignorance with regard to the powers and influence of all objects" when we consider them a priori, it follows that "there are no a priori bars on what types of events, properties, or entities might emerge from the causal interactions of complex groupings of micro-entities" (2000, p. 228). Nor can there be any bars on downward causation: for all we know, higher-level states such as final causes may be able to affect and even direct micro-level states. (Citing Arthur Lovejoy (1927), Cameron suggests that those who oppose emergentism do so because they unconsciously subscribe to a medieval "preformationist assumption" about causality: the doctrine that an effect is not understood until and unless "the eye of reason could somehow discern it in the cause" (2000, p. 228).)
Although I believe that Cameron has done a commendable job of arguing that it is metaphysical prejudice, rather than sound methodology, which underlies the scientific dismissal of teleological explanation, I would suggest that his account of teleological explanation leaves two major questions unanswered. First, there is the empirical question: exactly how can scientists tell which entities possess a telos or final cause? What kind of observations would a scientist need to make to confirm its presence?
Second, if final causes are an ontologically irreducible given, then why do we always look for non-finalistic explanations of biological mishaps such as death, injury and malformation? Why do material, formal or efficient causal explanations of these events seem satisfying while teleological explanations leave us dissatisfied? For instance, we can explain a person's death in: (a) efficient causal terms, whether positive ("She died as a result of a lightning strike") or negative ("She froze to death in Siberia after using up all the fuel in her portable stove"); (b) material terms, whether positive ("She died from a bacterial infection") or negative ("She died because she had lost too much blood"); (c) formal terms, whether at the organic level ("She died of a heart attack") or the genetic level ("She died as a result of a disease caused by a chromosomal anomaly"); or (d) temporal, thermodynamic terms ("She died of old age - or more precisely, the ends [telomeres] of the chromosomes in her body cells became so short as a result of accumulated wear-and-tear that her body cells could no longer replicate themselves"). Any of these explanations of death sounds perfectly all right, but the teleological explanation "She died because her body was no longer capable of functioning as it should, in accordance with its telos" leaves us wanting to ask: "Yes, but why was it no longer capable of doing so?" The foregoing examples suggest that teleological explanations, even if irreducible, need to be supplemented with lower-level explanations. The table below illustrates my point.
Table 1.6 - Explanations of death, injury and malformation invoking each of the five dimensions of life
|
Event: Mode of explanation |
Death of an organism | Injury to an organism | Malformation in an organism | Efficient causal explanation |
Positive:This animal died as a result of a lightning strike. Negative: This animal froze to death. |
Positive: This animal was injured by a falling rock, which broke its leg. Negative: This animal is suffering from rickets caused by a lack of sunlight. |
Positive: This animal's limbs are malformed because its mother was exposed to a toxic chemical while pregnant. Negative: This animal's limbs are malformed because its oxygen supply was partially cut off while its mother was pregnant. |
Material explanation |
Positive: This animal died of a septic infection caused by bacteria. Negative: This animal died because it lost too much blood from a wound it sustained in a fight. |
Positive: This animal has a septic infection as a result of foreign matter entering an open sore in its body. Negative: This animal is in a weakened condition because it has lost a lot of blood. |
Positive: This animal's limbs are malformed because either the sperm and/or the ovum from which it was generated was defective in some way. Negative: This animal's limbs are malformed because it suffered from malnutrition during infancy. |
Formal explanation |
Organic: This animal died of a heart attack. Genetic: This animal died as a result of a disease caused by a chromosmal anomaly. |
Organic: This animal is suffering from a progressive form of heart disease. Genetic: This animal is suffering from a disease caused by a genetic defect. |
Genetic: This animal's organs are malformed because of a deleterious mutation in its DNA. | Temporal (thermodynamic) explanation | This animal died of old age. At the tips of the chromosomes in the animal's cells are telomeres, repeating sequences of genetic material that shorten each time a cell divides. Cell division is important because many cells in an animal's body must be replaced over time. When a cell's telomeres reach a critically short length, however, that cell can no longer replicate, and its structure and function begin to fail. The process of telomere shortening may be likened to a genetic biological clock that winds down over time. | This animal acquired cancer as a result of accumulated cell damage over the course of a lifetime. | Genetic defects are more common in animal babies born to older mothers, whose ova may have been damaged over the course of decades by random events in their environment (e.g. background radiation). | Finalistic (teleological) explanation | This animal died because its body could no longer achieve its telos (or: because could no longer function properly). My response: yes, but why couldn't it do so? | This animal's arm is broken because the arm could no longer realise its telos (or: could no longer function properly). My response: yes, but why did it stop functioning properly? | This animal is malformed because it failed to develop according to its telos. My response: yes, but what went wrong during its development? |
My account of life, in a nutshell
What I am suggesting is that living systems are distinguished, not by their functionality (or what they do), but by how they do it. The account of life which I am proposing here can be summarised in the following eight points:
(i) two fundamental but inter-related causal features serve to distinguish living things from non-living things: their unique formal properties and their possession of intrinsic final ends. Moreover, the association between these two sets of features is not a contingent one: necessarily, any entity instantiating the relevant formal features also possesses intrinsic final ends, and vice versa. However, since the formal features cannot be understood without reference to finalistic concepts, a purely formal characterisation of life could never succeed;The account I am defending here has much in common with Cameron's (2000) teleological account of life, in which the property of being alive is defined as the possession of intrinsic ends. Cameron considers intrinsic finality to be both an ontologically primitive property and a strongly emergent one: its (final) causal features cannot be reductively identified with any properties of its structural components.(ii) there are empirical criteria, which have already been mentioned in the literature, that would enable scientists to discover which things instantiate these unique formal and final properties, and hence ascertain which things are alive;
(iii) final causality supervenes upon other kinds of causality (especially formal causality), but the property of being directed towards an end cannot be reductively identified with any lower-level property, in any unacceptably strong sense ;
(iv) teleological properties of organisms are, however, strongly ontologically emergent properties, which enable organisms to instantiate both downward and backward causation; however, these forms of causation supervene upon micro-level, forward causal properties;
(v) the distinction between having intrinsic ends and merely extrinsic ends is a real one, which allows us to clearly distinguish organisms from contemporary artifacts, which are in no sense "alive". However, there is nothing to prevent future scientists from constructing an artifact that possessed genuine intrinsic ends. Such an artifact would be alive;
(vi) a teleological account that equates "being alive" with possessing intrinsic ends is a complete, all-inclusive account, insofar as it explains the unity of "life" as a natural category (thereby solving what Cameron (2000, p. 50) refers to as the problem of unity, and provides a unified theory of all of the necessary and sufficient conditions for being alive - i.e. the (efficient, material, formal and final) causal conditions for an entity's being alive, as well as their temporal (i.e. thermodynamic and evolutionary) features;
(vii) the teleological account of life that I am proposing also allows us to formulate a robust concept of the nature of a living organism, in a way that is fully compatible with Darwinism;
(viii) finally, the teleological account of life being defended here is able to generate biological and moral norms.
The issues on which I part company with Cameron are the possibility of specifying formal criteria for an entity's being alive, and the question of whether final causality supervenes upon the lower-level (efficient causal, formal and material) properties supporting it. Cameron regards any attempt to specify non-teleological criteria which would enable scientists to identify life as reductionist - a point which I vigorously contest. I also maintain that purely teleological criteria for life are scientifically useless, as they cannot tell scientists which things are alive and which are not. On the issue of supervenience, Cameron appears to be inconsistent: he rejects the word "supervenience" but is happy to accept certain (non-identifying) forms of reduction that amount to the same thing. I suggest that his usage of "supervenience" is a non-standard one.
While Cameron can justly claim that his account solves the problem of unity which he describes (2000, p. 50), I have gone one step further with my teleological account: in section 1.4.6 and the Appendix, I attempt to show how intrinsic finality can unify all of the (efficient causal, formal, material and temporal) criteria for being alive, thereby satisfying the unity-of-criteria condition for life. I also argue that the formal criteria I propose for intrinsic finality allow us to re-interpret the Aristotelian concept of nature in a way which is fully compatible with Darwinism: the key, I suggest, is the Darwinian notion that species evolve very slowly, hence their ends change very little even over millions of years. The concept of an individual as having a certain nature can also generate biological norms regarding what it should and should not do, as well as moral norms for how we should and should not treat it.
I have endeavoured to put forward an account of life which: (a) meets scientists' (reasonable) demands for empirical criteria that allow them to identify life; (b) reconciles the best insights of Aristotle and Darwin; and (c) is consistent with the known facts.
It should be stressed that the foregoing account of life is intended to define life only in the biological sense of the word. My definition is thus limited to material entities which are amenable to scientific investigation. (Cameron (2000, p. 333) defends a general definition of "life" which can be applied in various senses to spontaneously generated organisms, plants, animals, humans and God.)
1.4.1 What distinguishes living things?
My first proposal, that form and finality distinguish living things, has strong Aristotelian roots. Aristotle (De Anima 2.1, 412a20-22, 28) defined the soul as "the form of a natural body which potentially has life, and since this substance is actuality, soul will be the actuality of such a body... [S]oul is the first actuality of a natural body which potentially has life" (1986, p. 157). Elsewhere (De Anima 2.4, 415b15, 20) he wrote that the soul was also the final cause, "that for whose sake" a living organism moves (1986, p. 165).
I claim that intrinsic finality is a unique feature of living things, and that it goes hand-in-hand with unique formal features which, characterise living things: a material object is alive and has intrinsic ends if, and only if, it possesses these features. However, as I explain in the following section, the formal features cannot be understood without reference to finalistic concepts, which is why a purely formal characterisation of life could never succeed.
The first part of my claim is not new. For instance, Cameron (2000, p. 333) defends a simple definition of life: to be alive is to possess intrinsic ends. (Cameron also identifies a secondary, derived sense in which an organ may be said to be alive, by being naturally connected with a being that possesses intrinsic ends.) Indeed, Cameron argues that this was Aristotle's original position - a contentious claim, which he defends vigorously and convincingly (2000, pp. 86-135) against an array of scholars who have construed Aristotle as holding that not only biological processes, but also necessary and regular occurrences in the inanimate world required final causes, or that all things possessing a nature had a final cause. Finally, Cameron argues (2000, pp. 327-335) that Aristotle was in fact well aware of the distinction between intrinsic and derived ends, insofar as he taught that the body parts of an organism possess ends, but only in a secondary sense which derives its intelligibility from the nature and finality of the organism as a whole.
My second claim, that the life-conferring property of possessing intrinsic ends is inseparable from the unique formal properties of living things, is a robust one. I do not claim that all of an organism's final ends can be determined or deduced simply by examining its formal features: for instance, the various functions of a walrus' tusks (protection against predators; acquisition of mating partners; getting a grip when climbing out of the water onto ice; and anchoring themselves on the ocean bottom while digging for clams) could never be guessed by someone who was unfamiliar with their local environment. What I do claim is that any material object instantiating all of the requisite formal features for being alive cannot fail to possess intrinsic ends, and that no material object can be said to have intrinsic ends unless it satisfies all of the required formal conditions.
My second claim is a controversial one, which Cameron (2000, pp. 145, 328) explicitly rejects. While granting the "coextensiveness in normal cases" of organisms' formal and final causal properties, he considers them separable in principle:
The formal causation of the growth of an organism is compatible with the absence of final causal influence; formal causation is therefore not sufficient for teleological causation (2000, p. 145).
Cameron puts forward three different reasons for rejecting the view that formal properties alone can confer intrinsic ends (and hence life) on an entity. First, he argues (2000, p. 146) that "[t]he mere fact that a good is forever associated with a process is no indication that the process occurs for the sake of the good". Logically, this is unassailable, but it is irrelevant to my own proposal, which is that a set of (lower-level) processes whose very nature enables their subject to benefit in some way (on a holistic level) can legitimately be described as being "for the good of" their subject.
Second, Cameron argues that complex artifacts such as robots, which are not alive, nevertheless display "the same sorts of material and structural complexity that organisms and living things display" (2000, p. 328). Following Paul Taylor (1986), Cameron distinguishes between the derived ends of complex artifacts and the intrinsic ends of biological organisms.
I regard Taylor's distinction between intrinsic and derived ends as a legitimate one (about which I shall say more below), but I would argue that Cameron is mistaken in maintaining that contemporary artifacts possess the same formal features as organisms. On the contrary, I contend that for an entity to be alive, the structural specifications of its parts need to be dedicated, from the bottom up, to supporting the proper functioning of the whole. As we shall see, contemporary artifacts are generally built in a top-down fashion, which prevents them from possessing the finality that characterises life-forms. However, future scientists might one day construct artifacts with the same "holistic" formal features as organisms. I shall argue that if they did so, the artifacts in questions would possess intrinsic ends and hence be alive.
A third argument of Cameron's against the view that the distinctive formal features of organisms are inseparable from their possession of intrinsic ends is that spontaneously formed inanimate objects exist in nature which instantiate the formal structures (and behaviour) of living organisms, while lacking their ends:
[F]or any sort of material structure that is claimed to ground teleology in biological systems, a materially identical counterpart can be found in systems which appear not to be teleological (2000, p. 154).
For instance, a wide range of mechanical systems possess feedback mechanisms which enable them to maintain a particular state, in the face of potentially destabilising environmental changes (2000, p. 174). Yet there is a vast gulf between the self-regulatory behaviour of these systems and the goal-directedness of organisms.
While I agree with Cameron that self-regulatory structures and/or behaviour do not confer intrinsic ends on an object, I shall argue below that it is not the stability of a structure, but those formal features that allow its parts to be dedicated to the support of the whole they comprise, that make it teleologically directed. While I concede that the structures discussed by Cameron lack ends, I claim that other structures do possess them as an in-built feature.
I have shown that Cameron's three grounds for supposing that non-living systems could instantiate all of the formal features of organisms while lacking ends are inconclusive. Furthermore, Cameron appears to contradict his own supposition (which I shall refer to as his "form-without-finality thesis") elsewhere in his work. Finally, I contend that this thesis is demonstrably false.
In his critique of the etiological account of functions, Cameron (2000, p. 185) approvingly cites the following remark by Richard Dawkins:
[A]ny engineer can recognize an object that has been designed, even poorly designed, for a purpose, and he can usually work out what that purpose is just by looking at the structure of the object (1986, p. 21, italics mine).
Dawkins later goes on to argue that Nature herself can be regarded as a "blind watchmaker". In any case, his point that the function of an object can be deduced from its structure is clearly at odds with Cameron's assertion (2000, pp. 145, 328) that an object could instantiate all of the structural features of an organism while lacking ends.
Additionally, Cameron's "form-without-finality" thesis leads to paradoxical conclusions. First, it would imply that there could exist a non-living duplicate of me, possessing my structural features yet lacking ends. Cameron himself contradicts this startling corollary of his "form-without-finality" thesis elsewhere in his work: he vigorously asserts (2000, pp. 198, 200) that a duplicate of me - even one created instantantaneously - would exhibit "purposive behaviours" and have bona fide functions, making it genuinely alive.
One way in which Cameron might attempt to avoid the charge of inconsistency here would be to argue that the possession of intrinsic ends is determined not by form alone, but by a combination of form and matter. Indeed, Cameron approvingly quotes Aristotle in support of his assertion - with which I agree - that"[b]eing alive depends upon possessing material composition of a very definite kind" (2000, p. 342). However, the reason why material composition is so critical is a formal one - a point recognised by Cameron himself:
Life, indeed appears to be dependent upon the existence of particular structurings of matter in exactly the way indicated for emergence (2000, p. 341).
(For instance, it is idle to speculate about whether a duplicate of me, in which the carbon atoms were replaced with silicon atoms, would be alive, as the structural possibilities of carbon and silicon atoms are very different: carbon dioxide is a gas, while silicon dioxide is a solid - sand.)
Second, Cameron's "form-without-finality" thesis calls into question the very enterprise of identifying something - a new species, or a purported life-form on another planet, for instance - as alive. If the formal features of an object do not determine whether it has an intrinsic end, how are we supposed to tell whether it has one? Cameron could perhaps argue that extended observation of the entity over a period of time is required to ascertain whether it possessed teleological features such as a life cycle, reproduction and so on - although this seems to be at odds with his assertion elsewhere (2000, pp. 198-200, 207-208) that an instant duplicate of me would be alive, or that we could readily identify the function of eyes and hearts even in instantaneously created lions that suddenly popped into existence. But the real difficulty with this "temporal solution" is that in practice biologists do not work like this: even though they may require an extended period of observation to determine what an organism's ends are (including its process of maturation), they do not stop there, but proceed to look for formal features of the organism (e.g. body clocks) that regulate these biological end-oriented processes.
It appears then, that the distinctive formal features of an organism cannot be separated from its aliveness. But that leaves us with two questions: how do we identify these features empirically, and why do we still need a teleological account of life if formal features enable us to distinguish living from non-living things?
1.4.2 Empirical formal and finalistic criteria for being alive
As we saw above, the empirical criteria commonly used to distinguish living things from inanimate objects are vulnerable to damaging counter-examples. Clearly we need more rigorous criteria for identifying life.
I believe that these criteria are already known to scientists. Indeed, most of them can be found in the long cluster definitions listed above. Sarver's (1999) definition of life lists seven conditions, of which the second and fourth - hierarchical organisation and a genetic program - when taken together, come closest to expressing why the distinction between "life" and "non-life" is a significant one.
Specifically, I suggest that the presence of both an Aristotelian formal cause and a final cause in a living body can be ascertained empirically by its possession of the following three biological properties:
The first two features would commonly be regarded as formal features of organisms, but as we shall see, they cannot be adequately characterised without reference to the telos of the organisms possessing them, so actually they could be described as both formal and finalistic; while the attribute of embedded functionality can be viewed as an empirical manifestation of both formal and final causality, insofar as it describes the manner in which the structured parts of an organism subserve the interests of the whole.
My claim, if correct, answers the first question in section 1.3.6: how can we tell if something is alive?
Why a master program?
The first of Koshland's "seven pillars of life" is a master program, i.e. "an organized plan that describes both the ingredients themselves and the kinetics of the interactions among ingredients as the living system persists through time" (2002, p. 2215). He goes on to say that for life on Earth, this program is implemented by DNA, which encodes genes, which in turn encode the chemicals that carry out the reactions for living systems. (Strictly speaking, our genome is programmed by the addition of chemical markers called methyl groups to the DNA, which can shut down genes (Motluk, 2004; Cohen, 2003).) (Recent research, reported in "New Scientist" (25 December 2002) has shown that RNA also controls key activities within cells.) I would suggest that the notion of a master program that governs the parts and their interactions is an appropriate way of expressing Aristotle's concept of a formal cause, in contemporary terminology.
(The proposal that a living organism's master program is a manifestation of its formal cause is not a new one: Hugh Lawson-Tancred, in a footnote to his Penguin translation of Aristotle's De Anima (1986, p. 238), cites a remark by Professor Max Delbrueck, that "if the Nobel committee were able to award the prize for biology posthumously, they should consider giving it to Aristotle for the discovery of the principle of DNA".)
From a philosophical prespective, the significance of the master program is that it confers a unity of form on the organism.
The term "master program" should not be misunderstood here. We are not talking about a program that regulates the entire suite of the organism's behaviour (towards the outside world), or even a program that maintains the organism in a state of homeostasis, but rather a program that controls the organism's internal structure and the internal interactions between its components. This is our core definition of an organism's formal cause, but broader definitions are possible.
(In a broader sense, we might define an organism's formal cause as the entire suite of programs responsible for directing the formation and preservation of an organism's structural features at all levels - whether at the cellular, tissue, organic or organismic level. In the broadest possible sense, the formal cause would include the set of all programs and physical structures within an organism which assist its survival.)
I claim that the possession of a master program is a necessary (but not sufficient) condition of a material object's being a living organism. This is a strong claim, unlike the more modest claim that all organisms possess a program(s) of some sort, which could easily be satisfied if we defined "program" in Wolfram's broad sense (2002, p. 383): all it would mean is that the behaviour of living things is constrained by rules. The requirement for a master program says something more: that the formation and preservation of the organism's structure should be regulated by a single, unified set of instructions (such as those contained in an organism's DNA), even if these instructions are widely dispersed through the organism's body. My reason for advancing this requirement is that an assortment of low-level programs working independently of one another, in the absence of any kind of central co-ordination, would be unable to accomplish their respective tasks smoothly and harmoniously, as they would be liable to interfere with one another. In particular, an assortment of independent programs could not be relied upon to accomplish two vital tasks: first, directing the formation of the organism's bodily structures during its development; and second, preserving the organism as a single, viable entity and and co-ordinating its activities.
However, the mere presence of a master program per se does not confer life on an entity, as it fails to explain why the entity should possess ends. I claim that in order to give rise to ends, the master program needs to be a very specific kind of program: one which generates a nested hierarchy of structure within the organism, and which also allows the functionality of the lowest levels to subserve that of the highest levels. Then and only then can we speak of the structure-as-a-whole as having ends of its own.
Why a nested hierarchy?
Allen (1996) provides a useful summary of the key concepts in hierarchy theory, a selection of which are reproduced in an appendix to this chapter. Briefly, what distinguishes nested from non-nested hierarchies is that the former involve levels which consist of, and contain, lower levels, while the latter do not. To use one of Allen's examples: an army is a nested hierarchy because it contains the soldiers which make it up, whereas the chain of military command is a non-nested hierarchy: a general does not "contain" the soldiers he/she commands.
A nested hierarchy of organisation is the second feature in Sarver's (1999) definition of life. I believe that this notion can be used to elucidate the meaning of Aristotle's concept of intrinsic finality. More precisely, a nested hierarchy is a necessary (but not sufficient) condition for intrinsic finality, because it is impossible to ascribe ends to an organism unless its parts work together for the benefit of the whole. To do this, the parts need to be hierarchically ordered. Finally, the hierarchy needs to be nested, in order for the parts to be intrinsically ordered towards the well-being of the whole. In a non-nested hierarchy, each part would be directed by some other part above and outside it; thus the part-whole finality would be merely extrinsic. The table below (taken from Allen, 1996) summarises the key concepts of hierarchy theory.
Table 1.7 - A Summary of the Principles of Hierarchy Theory
|
The Hierarchy theory is a dialect of general systems theory. It has emerged as part of a movement toward a general science of complexity. Rooted in the work of economist, Herbert Simon, chemist, Ilya Prigogine, and psychologist, Jean Piaget, hierarchy theory focuses upon levels of organization and issues of scale. There is significant emphasis upon the observer in the system.
Hierarchies occur in social systems, biological structures, and in the biological taxonomies. Since scholars and laypersons use hierarchy and hierarchical concepts commonly, it would seem reasonable to have a theory of hierarchies. Hierarchy theory uses a relatively small set of principles to keep track of the complex structure and a behavior of systems with multiple levels. A set of definitions and principles follows immediately: Hierarchy: in mathematical terms, it is a partially ordered set. In less austere terms, a hierarchy is a collection of parts with ordered asymmetric relationships inside a whole. That is to say, upper levels are above lower levels, and the relationship upwards is asymmetric with the relationships downwards. |
| Hierarchical levels: levels are populated by entities whose properties characterize the level in question. A given entity may belong to any number of levels, depending on the criteria used to link levels above and below. For example, an individual human being may be a member of the level i) human, ii) primate, iii) organism or iv) host of a parasite, depending on the relationship of the level in question to those above and below. |
| Level of organization: this type of level fits into its hierarchy by virtue of set of definitions that lock the level in question to those above and below. For example, a biological population level is an aggregate of entities from the organism level of organization, but it is only so by definition. There is no particular scale involved in the population level of organization, in that some organisms are larger than some populations, as in the case of skin parasites. |
| The ordering of levels: there are several criteria whereby other levels reside above lower levels. These criteria often run in parallel, but sometimes only one or a few of them apply. Upper levels are above lower levels by virtue of: 1) being the context of, 2) offering constraint to, 3) behaving more slowly at a lower frequency than, 4) being populated by entities with greater integrity and higher bond strength than, and 5), containing and being made of - lower levels. |
| Nested and non-nested hierarchies: nested hierarchies involve levels which consist of, and contain, lower levels. Non-nested hierarchies are more general in that the requirement of containment of lower levels is relaxed. For example, an army consists of a collection of soldiers and is made up of them. Thus an army is a nested hierarchy. On the other hand, the general at the top of a military command does not consist of his soldiers and so the military command is a non-nested hierarchy with regard to the soldiers in the army. Pecking orders and a food chains are also non-nested hierarchies. |
| Constraint versus possibilities: when one looks at a system there are two separate reasons behind what one sees. First, it is not possible to see something if the parts of the system cannot do what is required of them to achieve the arrangement in the whole. These are the limits of physical possibility. The limits of possibility come from lower levels in the hierarchy. The second entirely separate reason for what one sees is to do with what is allowed by the upper level constraints. An example here would be that mammals have five digits. There is no physical reason for mammals having five digits on their hands and feet, because it comes not from physical limits, but from the constraints of having a mammal heritage. Any number of the digits is possible within the physical limits, but in mammals only five digits are allowed by the biological constraints. Constraints come from above, while the limits as to what is possible come from below. The concept of hierarchy becomes confused unless one makes the distinction between limits from below and limits from above. The distinction between mechanisms below and purposes above turn on the issue of constraint versus possibility. Forget the distinction, and biology becomes pointlessly confused, impossibly complicated chemistry, while chemistry becomes unwieldy physics. |
The panexperientialist philosopher Charles Birch has made some interesting comments on how the unity of living organisms, which is reflected in their nested hierarchy, makes them fundamentally different from computers designed by human beings. He employs a distinction between internal and external relations to illustrate why human-built computers are aggregates rather than individuals:
In the Newtonian universe of mechanism there are only external relations between entities. Entities either push or pull one another around. External relations are incidental to the entity. Their occurrence or non-occurrence does not affect the being or character of the entity. The Newtonian universe is made of substances which by definition have an independent existence. The idea of an internal relation is of a relation which is constitutive of the character and even the existence of something... (2002, p. 6, italics mine).
It is not just that the whole is more than the sum of its parts. It is that parts become qualitatively different by being parts of a whole... According to the doctrine of internal relations the relations of one entity to others are constitutive of the entity in question... The bricks that are built into an office block remain the same if that office block is torn down and the bricks are assembled in a different architecture to make a cathedral. The brick is not an individual entity but an aggregate of individual entities... Not so for an atom in a molecule or a molecule in a cell or a cell in the liver or a cell in the brain... [For instance,] a carbon atom in diamond has different properties from a carbon atom in an enzyme... (2002, pp. 6-7, italics mine).
Birch (2002, p. 8) goes on to say that in a cell or an organism, unlike a computer, the components are "organised into a hierarchy of compound individuals". For Birch, it is this hierarchy of organisation which allows us to speak of the cell as a unity.
But this still does not bring us to the notion of intrinsic ends. A program that generates a hierarchically organised structure could be purely static. In an entity with intrinsic ends, the parts need to work for the good of the whole. To guarantee this, we need the added ingredient of embedded functionality.
Why embedded functionality?
The nested hierarchy of living things reflects a functionality in which the entire repertoire of the functionality of the parts is "dedicated" to supporting the functionality of the whole unit which they comprise. (By "the entire repertoire", I mean everything that the parts actually do, not everything they can do. The parts of a unit may have other potential uses: genes and even organelles can be exchanged between organisms, as shown by the phenomena of lateral gene transfer and endosymbiosis, respectively.)
Geer (2002) quotes the following explanation of the concept of embedded functionality by Dr James Tour, the Chao professor of chemistry and computer science at Rice University:
Dr. Tour explains: "[Let's say that] you see a tree [and] you want to make a table, [so] you chop down the tree [and] you make a table - that's [building] top down. But, the tree and I and everything else in nature are built from the bottom up. Molecules have certain embedded interactions between them and embedded functionality. Those come together to form higher-order structures called cells and those form higher-order structures and here we are." You might also envision this as building from the inside out, or by forming the required traits in the smallest conceivable building blocks first.
This "dedicated" functionality, the product of four billion years of evolution, can be seen at every level of organisation of a living thing, from the bottom up. Living things are built from the bottom up, by "dedicated", intrinsically adapted parts; today's human-built computers are designed from the top down, out of parts which have to be modified in some way, to suit the designers' ends.
Embedded functionality is by no means unique to living things: as we saw, it is found in molecules too. However, what I am suggesting is that all organisms, and only organisms, possess the combination of a master program that directs the generation of a nested hierarchical structure with the property of embedded functionality.
Entities with these specific formal features are guaranteed to possess intrinsic ends, because the parts work in a way that subserves the good-of-the-whole in a way that is built-in, and not merely accidental.
1.4.3 Is my account of life reductionistic?
I do not believe that final causality in an organism can be somehow reduced to the three features just described. The reason why any reductive project is bound to fail is that the ends possessed by organisms are holistic ends, and no lower-level description of a biological process, however complete it may be, can be equated in meaning with a holistic description of the same process, even if the two descriptions are truth-functionally equivalent. It is for this reason that Mayr (1982) rejects the simplistic assertion by what he calls strong mechanists, that organisms are nothing but chemical machines, whose properties and parts are wholly reductively identifiable with and explicable in terms of the laws of physics and chemistry.
Another reason why final explanations are not reducible to formal ones is that such a reduction incorrectly assumes that we can describe the formal features of a living organism using non-teleological terminology. But when we are talking about organisms, it is impossible to compartmentalise our language regarding formal and final causality in this way: the two forms of causality are inextricable. We cannot, for instance, properly describe an embedded functionality without reference to its ends. An although an inanimate object could contain a master program or nested hierarchy of organisation in the absence of embedded functionality, even these formal features, when realised in an organism, cannot be properly described without reference to the ends that they enable the organism to achieve.
I would also like to emphasise that I do not claim that an organism's final cause is nothing more than the part-whole functionality of its bodily organs. As Cameron points out (2000, p. 149), organisms possess not one but a variety of holistic ends, such as reproduction, developing into mature adults, and their own individual flourishing. The way in which an individual's body parts are subordinated to the whole can tell us a lot about the individual's flourishing, but it is clearly inadequate to characterise the processes of maturation and reproduction, both of which involve reference to future states - whether of the organism or its progeny. On the other hand, I do believe that an organism's ability to realise all of these ends supervenes upon a combination of the three biological features I listed above.
As I mentioned above, one point where I part company with Cameron is that I regard final causality as supervening upon the other forms of causality - especially formal causality. Mandik (2004) defines supervenience as follows: "[a] set of properties or facts M supervenes on a set of properties or facts P if and only if there can be no changes or differences in M without there being changes or differences in P". It follows that if two individuals have the same formal, material and causal properties, then on my account of final causality, either both of them have a telos (intrinsic end) or neither of them has one. Cameron appears to reject this assertion: he clearly states that "[e]mergentists do not conceive of downward causation on the model of supervenience" (2000, p. 243) and later explicitly asserts that "[e]mergence is also opposed to the thesis ('Humean supervenience') that all of the properties of wholes are determined by the local intrinsic properties of micro parts" (2000, p. 256).
On this point, it seems that Cameron is not wholly consistent: later, he writes:
[T]here is a sense in which ontological emergentists are emphatic not to deny that emergent properties are 'determined by' their basal conditions; claims of ontological emergence are even compatible with the claim that the behavior of wholes with emergent properties is wholly determined by the laws governing the behavior of the elements in the basal conditions (2000, p. 258).
If Cameron is willing to accept the claim he refers to above, then I would consider him as endorsing supervenience. I suspect this is his actual position, and that he is simply using an odd, non-standard definition of supervenience: after commenting that emergence is opposed to the thesis of Humean supervenience, he writes that "emergentists thus reject ... the doctrine of particularism: [T]he conception of natural events as combinations or rearrangements of relatively simple, preexistent entities, of which the total number or quantity remains invariant, and of each of which the qualities and laws of action remain the same through all the combinations into which it may enter" (2000, p. 256, italics mine). It seems that Cameron uses the word "supervenience" to denote philosophical atomism.
That Cameron regards his philosophical position as compatible with supervenience (in the standard sense of the word) is readily apparent from his remark (2000, p. 270) that even the successful reduction by atomic theory of "water" to H2O is compatible with water's properties (its wetness, boiling point) being emergent properties of H2O molecules. Although the properties of water are not identical with the properties of its constituent molecules, it is certainly true that in ordinary parlance, the properties of water supervene upon the properties of its constituent molecules. The only kind of reduction which Cameron (2000, p. 271) rejects as incompatible with emergence is reduction by property identity, where being F is identical to instantiating some set of properties G1,....Gn in some relation R. In this sense, the property of temperature (for ideal gases) has been reduced to the mean kinetic energy of the constituent molecules: the two properties are the same.
If final causality supervenes upon the other forms of causality, then we can answer the second question in section 1.3.6: we look for micro-level, non-finalistic explanations of death and injury because macro-level, finalistic descriptions supervene upon micro-level, non-finalistic descriptions. However, these explanations, while more basic, can never tell the whole story of what happens when an organism dies or is injured, as they are incapable of encompassing its built-in holistic ends.
1.4.4 Strong emergence, downward and backward causation
I argued in section 1.4.1 that the denial of the supervenience of final causality upon other forms of causality generated paradoxes - such as the possibility of there being an inanimate duplicate of me - which even Cameron was not willing to accept (2000, pp. 198, 200). In this section, I argue that supervenience is fully compatible with strong ontological emergence, according to Cameron's definition, as well as downward and backward causation.
Table 1.8 Some definitions pertaining to strong and weak emergence (Cameron, 2000, pp. 278-279)
| The core sense of emergence: A property P of a structure X with components a1, ... an is emergent if and only if (i) P depends causally for its existence on the interactions of a1, ... an in X and (ii) P augments the ontology of the world - P is not "contained in" the properties of a1, ... an in their interactions outside of structures of the same type as X. |
| Basal conditions: The basal conditions of a complex thing "include just the qualitative, intrinsic properties and relations of the parts, i.e., the properties and relations that these bear in and of themselves, without regard to any other objects, and irrespective of any further consequences of their bearing these properties for the properties of any wholes they might compose" (Healey 1991, 401). |
| Additivity: A property F is an additive property if it is a property of a complex system S composed of parts and properties P1...Pn, and none of P1...Pn has F. |
| Novelty*: A property P of a complex physical entity E of type T, where entities of type T possess basal conditions B composed of parts, properties and relations b1...bn, is novel if and only if (i) P depends causally for its existence on the interactions of b1...bn, and (ii) P is irreducibly different in kind from the kinds of properties and relations had by the component parts b1...bn of the basal conditions B as they appear independent of their composing entities of type T; that is, (ii') P cannot be reductively identified with any of the kinds of properties and relations had by the component parts b1...bn of the basal conditions B as they appear independent of their composing entities of type T. |
| Mere resultants: A property P of a complex physical entity E of type T, where entities of type T possess basal conditions B composed of parts, properties and relations b1...bn, is merely resultant if and only if it is additive but not novel. |
| Weak ontological emergence: A property P of a structure X with components a1...an is weakly ontologically emergent if, and only if P is novel*. |
| Strong ontological emergence: A property P of a structure X with components a1...an is strongly ontologically emergent if and only if (i) P is novel* and (ii) P has causal powers which are absent from a1...an and their interactions independently of entities of the same type as X. |
On Cameron's definition, final causality - as I construe it - is a novel* property of organisms, because it depends on the interactions between the parts of an organism, but is irreducibly different in kind from the properties of the parts: as we argued above, finality cannot be reduced to some combination of efficient, formal and material causality. Thus it is at least a weakly emergent property. Additionally, it has causal powers which are absent from the parts of an organism, when these parts are not configured as organisms, making it strongly emergent. However, I argued in section 1.4.3 that final causality supervenes upon other forms of causality. I conclude that supervenience is compatible with strong ontological emergence.
The notion that macro-level events might somehow determine micro-level processes remains a highly suspect one for many scientists and philosophers, and is often criticised for being "too mysterious". Cameron (2000, pp. 230-232, 240-243) addresses this objection at length, arguing that the same could be said for any causal relation:
No empirically discovered causal relation must pass before the bar of a priori reason's demand that it be made 'transparent' to the mind before we may accept it into our ontology. No causal relation, upwards, downwards, or horizontal is anything but opaque to our reasoning. The invocation of mystery ... is wholly out of place (or rather, time) in a post-Humean context (2000, p. 243).
As we have seen, Cameron regards downward causation as incompatible with supervenience:
As the emergentists use the word, macro-to-micro determination is a causal relation; macro events are related as causes to micro events as effects. Often, however, micro-to-macro determination may be thought of not as a causal relation at all, but as a logical or supervenience relation, as when we say that the dots in a dot-matrix picture determine the picture's qualities... Emergentists do not conceive of downward causation on the model of supervenience, they understand it as an instance of ordinary causal relations between things and events in the world (2000, p. 243).
I disagree with the implicit suggestion here that emergence and supervenience are incompatible. For the crucial feature of an emergentist account, in condition (iv) of Cameron's definition above, was that "the 'emergent' parts or properties ... exert 'their own' causal influence over the course of their microparts' careers without breaking laws governing the behavior of microparts and properties." In other words, causal powers at the macro-level are irreducible to those at the micro-level. But the fact that the macro-level causal powers of an organism supervene upon the causal powers of its micro-level parts, does not mean that the macro-level causal powers can be explained from below. Nor does it imply that the causal powers of the organism are exhausted by thos of its parts.
The reason why supervenience is compatible with emergence is that no micro-level description of the parts of an organism and their interactions can explain the organism's wholeness and teleological unity, or its ability to have intrinsic ends. To formulate such an explanation we need to view the organism at the holistic level: at lower levels, one cannot see the wood for the trees. At the holistic level, it is quite legitimate to speak of biological processes within the organism as being directed towards its future ends (such as maturation or reproduction), even if the organism's ability to achieve these ends supervenes upon its micro-level structural features. The end controls the process, not only in the counterfactual sense that if it were not there, the process would not occur (for if one accepts supervenience, the absence of an end would mean that the micro-level structural features would have to be different), but also in the stronger sense that the end possess a reality of its own that cannot be reduced to the efficient, formal and material causal features of the organism, and it is this reality which renders the process intelligible. In this sense, backward causation is quite real. Downward causation presents even less of a problem, as the processes in the parts are directed not at future states but at the present welfare of the whole.
Cameron has, I suggest, been misled by his own dot-matrix picture metaphor of supervenience (2000, p. 243). A dot-matrix picture is a poor analogue of supervenience, as it lacks irreducible higher-level properties: all of its features can be explained reductively, in terms of the spatial relations between the dots.
1.4.5 Is the possession of intrinsic ends a sufficient and necessary condition for being alive?
Intrinsic versus extrinsic finality: Is the distinction a clearcut one?
The relevance of the distinction between intrinsic and extrinsic finality has been contested by some philosophers. Leahy has argued that the distinction is blurred by human domestication of animals:
Furthermore it is not even clear that the distinction in telos is that marked. What is in the interests of animals is increasingly decided by human beings. A good guide-dog, sheep-dog, circus, zoo or farm animal, thoroughbred or pet siamese is treated on the basis of criteria proper to the different roles imposed upon them by human beings... (1994, p. 46).
The recent introduction of genetically modified organisms, which are expressly created for human ends, may seem to buttress Leahy's case. However, there is nothing to prevent an organism's having both intrinsic and extrinsic ends. My contention is that it is only in virtue of the former that it can be said to be alive.
Another critic of the distinction between intrinsic and extrinsic finality is Varner. Although he recognises the distinction between artifacts and living things as one which matters philosophically and ethically, Varner is leery of resorting to an extrinsic vs. intrinsic dichotomy to ground this distinction. Citing Nagel, he argues (1998, p. 66) that some artifacts can be regarded as "goal-directed systems" with ends that can be specified independently of the goals of their human producers. To illustrate his case, he offers the example of a Patriot missile, uncovered by an alien scientist long after a nuclear holocaust has wiped out all intelligent life on earth. The alien may be able to deduce that Patriot missiles are meant to intercept projectiles, without knowing a thing about late 20th century aerial warfare.
(We can strengthen Varner's case by imagining a 21st century new generation missile, with unforeseen military capabilities, designed and refined not by human beings but by a factory of robots, following the instructions of a computer, after all human life on earth has been wiped out in a nuclear conflict. Let us say that the computer was originally programmed by a long-dead mathematician, not to build a particular missile, but to follow a search algorithm for identifying and comparing possible designs for missiles. In this case, the design is actually "found" by the computer, and its capabilities were not foreseen by the program designer, so its built-in ends cannot be adequately specified in terms of the intentions of the human designer of the original search algorithm.)
A few comments are in order here. First, the Patriot missile does not have an internal master program that regulates its formation and the structure of its internal parts. Instead, what it has is a built-in program that co-ordinates its internal parts, after they have been assembled by some externally directed process. In a very real sense, then, its ends, though built-in, are not intrinsic to it. Living things, by contrast, are self-assembling.
Second, while the missile has a built-in goal, the parts appear to be linked by what Birch (2002) calls external relations. Unlike the biomolecules in a cell, the missile parts do not acquire any new physical properties by virtue of being put together; rather, the missile is an assemblage of pre-existing parts whose properties can be described in isolation from one another, and the workings of the ensemble can be subsequently deduced from an understanding of these external properties alone. To use one of Birch's similes (2002, p. 7), the relation between the parts is like that between the bricks in an office block. (It is likely that the parts of living things mesh together in a way that permits internal relations, for historical reasons: they evolved together, and acquired their features because they had to co-ordinate with each other.)
Third, even if there were internal relations between the missile parts, this would not be a sufficient condition for the missile to possess intrinsic finality. They would also have to possess a nested hierarchy of organisation. Birch (2002) explains the rationale for this requirement:
The most complex computer designed for AI will always be a machine and not an organism in any real sense. The parts of the computer are not organisms like cells in the brain. The total computer is an aggregate and not an individual entity. Aggregates such as computers and motor cars have lots of properties, but they do not have the property of a unified experience... [Their] components are not organised into a hierarchy of compound individuals (2002, p. 8, italics mine).
What Birch is claiming here is that living things have a property that makes them fundamentally different from computers: the relation of the parts to the whole. In a living thing, not only do the parts acquire new physical properties when they are organised into a whole, but they are also organised in a nested hierarchy, from macromolecules to organelles to cells to tissues to organs to organisms. It is this hierarchy which allows us to say that the telos of the parts is completely subsumed within that of the whole. Because human-built computers (and Patriot missiles) lack not only internal relations but also hierarchy of internal organisation, they are, as Birch remarks, mere aggregates, not individuals.
Fourth, the functionality (or range of activities) of the parts of an entity possessing intrinsic finality needs to be dedicated, in such a way that it can only be understood by reference to the whole. For each layer in the nested hierarchy of a living thing, the repertoire of functions of the parts supports the next highest level of organisation. No such dedicated functionality exists in a Patriot missile, or in today's computers.
Finally, while it may be true that certain goal-directed features of artifacts can be appreciated without a knowledge of what they were designed for, the point remains that these artifacts are not self-directed. In Varner's example, the parts are not designed to maintain the missile, but to enable it to shoot down projectiles. The missile does not "benefit" in any sense from doing so - its mission is a "suicidal" one. Its finality is thus extrinsic, rather than intrinsic. (Likewise, a computer designed by human beings has a telos, but it is extrinsic: it is designed to perform computations.)
Why should intrinsic finality be a sufficient and necessary condition for life?
It has been argued that teleology is a defining feature of life, that the distinction between intrinsic and extrinsic finality is a valid one and that there are well-defined empirical criteria for identifying entities which instantiate intrinsic finality. However, we still need to defend the claim put forward in section 1.4.1, that intrinsic finality is a sufficient condition for being alive. We saw in section 1.3.1 that single-attribute definitions of life were vulnerable to counter-examples. Why, it may be asked, should this single-attribute definition be any different? And why should we look for a single defining attribute, anyway?
My answer is that only a single attribute definition of life can be a philosophically satisfying one. As we saw in section 1.3.2, the alternative is to accept some variety of cluster definition. However, cluster definitions are inherently unsatisfactory: they are incapable of satisfying the unity-of-criteria condition (that is, they cannot explain why the assorted criteria listed, and no others, are criteria for life) and they fail to solve Cameron's problem of unity (that is, they cannot tell us why the term "life" should apply to all living things, and only to those things). A unified definition of life is therefore vastly preferable to a looser cluster account, which Bedau describes as "a fall-back position that can be justified only after all candidate unified views [of life] have failed" (1996, p. 336).
In section 1.3.1, we concluded that of the three kinds of challenges faced by single attribute definitions of life - counter-examples, borderline cases and category challenges - only the first posed a real problem. The issue of whether intrinsic finality is sufficient to define "life" stands or falls on the question of whether there are any things that instantiate this feature and that we would not describe as alive, while the issue of its necessity hangs on the question of whether there are any things we would call alive, but which lack intrinsic finality.
There seem to be no valid counter-examples to the sufficiency of intrinsic finality. Any valid counter-example would either have to be a natural object or an artifact. It has been argued in this section that no contemporary artifact even comes close to instantiating the formal requirements for intrinsic finality (i.e. a master program, a nested hierarchy and embedded functionality). Crystals and flames seem to be the closest non-living natural objects to living things, in behavioural terms. However, neither crystals nor flames satisfy the formal requirements for intrinsic finality, described above.
It is certainly true (as I argue below) that future artifacts could indeed possess the property of intrinsic finality. However, we cannot regard these artifacts as valid counter-examples unless we make the question-begging assumption that anything built by human beings entirely out of non-living materials is inanimate. While it is commonly agreed that existing artifacts are not alive - a fact which can be explained on a teleological account, by their lack of intrinsic finality - there is no general agreement that artifacts constructed from non-living components cannot in principle be alive.
The sufficiency of intrinsic finality appears secure. We now have to ask whether there are any things lacking intrinsic finality, but which we would normally call alive. In fact, there do not appear to be any such cases. Teleonomic behaviour, described by Monod (1971) and Mayr (1982) as a feature of living things, appears to be a universal property of life: it can readily be discerned not only in plants and animals, but also in unicellular (one-celled) organisms. Even viruses possess this property, as I argue below in the Appendix.
I conclude that no valid counter-examples can be adduced against the hypothesis that intrinsic finality is a necessary and sufficient feature of living things. If (as I argue below in section 1.4.6), the property of intrinsic finality manages to satisfy the unity-of-criteria condition and solve Cameron's problem of unity, then we should regard the necessity and sufficiency of this property as philosophically established: there is no more philosophical "work" that it needs to do, and there is no other rival contender that can do the work it does.
Can artifacts instantiate intrinsic finality?
There is no reason in principle why a computational device could not be designed from the bottom up, out of chemical parts which acquire new physical properties when assembled (like the carbon atoms in a benzene molecule), and which exhibit the properties of a nested hierarchy of organisation and dedicated functionality. Indeed, a report (Geer, 2002) in "Techworthy" computer magazine quotes Dr. James Tour, Chao professor of chemistry and professor of computer science at Rice University, as claiming that the science of nanotechnology permits the possibility of constructing computers in this way.
Dr. Tour explains: "[Let's say that] you see a tree [and] you want to make a table, [so] you chop down the tree [and] you make a table - that's [building] top down. But, the tree and I and everything else in nature are built from the bottom up. Molecules have certain embedded interactions between them and embedded functionality. Those come together to form higher-order structures called cells and those form higher-order structures and here we are." You might also envision this as building from the inside out, or by forming the required traits in the smallest conceivable building blocks first.
"Nanotechnology," says Dr. Tour, "allows building from the bottom up in this way. You put within the molecule, you program within the molecule, you embed within the molecule, certain structure that gives you memory function, which gives you switching function. That will allow this molecule to hold onto electrons, to be your memory. That will allow this molecule to be in either one of two possible states, so you have your switch.
"Then you build little groups on the ends of the molecules, that we call alligator clips (conveniently), that will then hook these molecules onto probes. So, you do that all within molecules, but you make 1023 molecules at a time. Then you learn how to self-assemble them. You build within them a structure that causes them to line up next to their neighbor on a surface, so that now you make higher order structure from disorder, just by dipping in a substrate and pulling it out. Now covering the surface are molecules all lined up and in order. That's bottom up as opposed to top down. That's what Nanotechnology offers."
Additionally, the field of organic computing is likely to blur the boundaries between living things and human-built computers in the foreseeable future. Geer's (2002) report also cites research by Dr. Leonard Adelman, who proposed in 1994 that DNA molecules could be used to solve difficult computational problems, and demonstrated the usefulness of DNA in computing. For example, mathematical problems can be solved very rapidly by insinuating mathematical questions into the DNA code and embedding them in the chemical reactions that occur among DNA.
It should be borne in mind, however, that a DNA molecule, by itself, is not "alive" in the sense that I have defined above: although it is the key molecule for life on earth, it does not display the nesting hierarchy observed in living cells, let alone embedded functionality. (The related question of whether viruses, which are not composed of cells, but of DNA wrapped in a protein coating, can be said to be alive will be discussed below.)
Returning to the question of whether computers built by human beings could ever be said to be alive: it is certainly possible that a computational device could one day be designed with a master program regulating the internal parts that were produced and the interactions between them, where the parts of the device were linked by internal rather than external relations, with a nested hierarchy of dedicated functionality, supporting the continued existence of the system. Such a device could then be said to have a good of its own (i.e. intrinsic finality) by virtue of its form, and could therefore be described as alive, if it also possessed a concrete material realisation (i.e. a material cause). It needs hardly be said that such a device would be very different from today's human-built computers.
1.4.6. Does my account of life explain and unify all of the necessary conditions for something's being alive?
1.4.6(a) Does my account of life unify the necessary conditions for something's being alive?
As we saw above, cluster definitions of life fail to satisfy the unity-of-criteria condition, and they fail to solve what Cameron calls the problem of unity (2000, p. 50). In other words, they fail to provide a unified explanation of why some criteria, but not others, are part of the definition of life, and why some entities are classified as alive, while others are excluded. The demand for such an explanation appear to be reasonable, as "life" is supposed to designate a natural category.
If the Aristotelian account of life being defended here is superior to the cluster accounts we examined above, then it must satsify these two definitional requirements as well. At first, Aristotle's account appears vulnerable to Cameron's problem of unity, since it defines as alive any being possessing one or more of the following powers, corresponding to various faculties of the principle of life (soul): "thought; perception; motion and rest with respect to place; and further motion with respect to nourishment, decay and growth" (De Anima ii.2 413a20-26). The selection of powers appears arbitrary. One might ask: what makes entities instantiating these powers so special? However, Cameron argues that Aristotle, despite regarding the property of life as multivocal, was able to account for the unity of life in teleological terms: to be alive is to possess intrinsic ends (2000, p. 333). What the different faculties of the soul have in common is that they enable living things to realise their own good.
Now that Aristotle's account has been shown to solve the problem of unity, we can address some of the counter-examples raised earlier against two criteria invoked by Aristotle (De Anima 2.4) as distinguishing features of life - namely, nutrition or reproduction. We saw earlier that these features were unsuitable for formulating single-attribute definitions of life: for instance, even flames can reproduce and crystals can grow. However, inanimate objects that "grow" and "reproduce" cannot meaningfully be said to do so for their own good, as they fail to satisfy the three formal requirements discussed above for having a good of one's own (i.e. for possessing intrinsic ends). Thus nutrition and reproduction, considered in isolation, cannot serve to define life, but when they are re-defined as teleonomic activities occurring in physical entities possessing intrinsic ends, they can be regarded as hallmarks of life.
Although the problem of unity has been addressed by providing a unifying teleonomic account of the various sorts of activities that occur in different kinds of living things, we are still left with the unity-of-criteria requirement described earlier. What we need is an account that unifies all of the criteria we use to determine whether something is alive or not - i.e., the necessary and sufficient conditions for life. Without some account that encompasses all of these conditions, scientists and philosophers are left once more with an untidy cluster of requirements for life, which suggests to some thinkers (Wolfram, 2002) that the term "life" designates an arbitrary category rather than a natural one.
Before I attempt to provide a unifying account of these conditions along teleological lines, I need to explain why an alternative, non-teleological account would not be viable. The most obvious rival contender would be a formal account, as the form of a living thing confers on it a kind of unity. The problem with a formal unification of the conditions for life is that there is no single formal condition which defines "life". Instead, as we saw earlier, there are three distinct formal criteria which, taken together, constitute sufficient conditions for being alive: a master program that directs the formation of and interactions between the parts; a nested hierarchy of organisation; and embedded functionality. We need to know what these formal requirements for life have in common: why these three, and only these three?
The prospect of developing a unifying account of life in terms of any of the other "dimensions" (material, efficient causal or temporal) appears even more remote. None of these dimensions deals with organisms at the holistic level, as living individuals; instead, scientists employ a reductionist methodology to describe the properties of life along these dimensions.
I conclude that only a teleological account offers a reasonable prospect of being able to encompass all of the criteria we use to identify something as being "alive".
The teleological account I wish to defend here is that all of the formal, material, efficient causal and temporal conditions for something's being alive are simply requirements that any material entity must satisfy in order to be able to realise intrinsic ends (of whatever sort), given the laws of nature in our universe. I have included a proviso regarding the laws of nature because in a world with different laws, the necessary conditions for being alive would be very different.
On my proposal, the formal conditions for being alive are simply informational and structural requirements that any physical entity must satisfy before it can be regarded as having an end or telos of its own, namely: (i) a master program to direct its formation and co-ordinate its activities; (ii) a nested hierarchy of organisation that subordinates the parts to the whole they belong to; and (iii) embedded functionality, which guarantees that the activity of the parts is dedicated to the good of the whole. The "common thread" uniting these conditions is that if any of them were not realised, the entity would no longer be capable of teleonomic behaviour, and hence would be unable to realise any ends of its own.
If, however, all of the above formal conditions are realised by a physical entity, then the behaviour of the entity cannot fail to be teleonomic: the entity is inherently capable of doing things for itself. Thus no "extra" formal conditions are needed.
There may, however, be lower-level formal requirements that an entity must satisfy in order to meet conditions (i), (ii) and (iii). Indeed, I shall argue below that some of the seven "pillars of life" stipulated by Koshland (2002) are actually low-level formal requirements that serve to guarantee the integrity of living cells.
On the account I am developing, the material conditions for being alive are those which enable an entity to possess intrinsic ends. Specifically, the material conditions are the physical requirements an entity must satisfy in order to possess an appropriate form - i.e. one which meets the three conditions described above.
The efficient causal conditions for life can be defined as the set of interactions that must take place between between a physical entity and its environment in order for it to achieve those intrinsic ends (such as nutrition and reproduction) which are common to all organisms.
Finally, the temporal conditions for life are simply those which an individual organism or lineage of organisms must satisfy, in order to continue achieving its own ends over a prolonged period of time. Given the laws of nature in our universe, an organism (or lineage of organisms) is likely to encounter certain potentially destructive changes over the course of time, so it needs to be able to combat or cope with them. Specifically, organisms and lineages of organisms need to be able to withstand the onslaught of entropy and to adjust to ongoing environmental changes. These requirements generate the thermodynamic conditions and the evolutionary conditions for life, respectively.
In the following discussion of the necessary conditions for life, I shall focus particularly on former "Science" editor-in-chief Daniel Koshland's "seven pillars of life" (2002), which I propose to classify according to the "five-dimensional" scheme described earlier. (I have already discussed the first of Koshland's pillars, a master program.)
1.4.6(b) What are the necessary conditions for something's being alive?
Material requirements
Concrete material realisation
My stipulation of a concrete material realisation as a necessary condition for being alive harks back to Aristotle, who, it will be recalled, refers (De Anima 2.1, 412a20) to the soul as "the form of a natural body" (1986, p. 157, italics mine). As he puts it (De Anima 2.1, 412a19):
For the body, far from being one of the things said of a subject, stands rather itself as subject and is matter (1986, p. 157).
The importance of a concrete material realisation is that it individuates an entity, making it a single subject. Without a material realisation, the entity, having no spatio-temporal location, could not properly be described as a single individual. An entity with purely formal properties would lack a specific "thisness" about it. Lacking individuality, it could not meaningfully be described as benefiting or as being harmed, as no specific (spatio-temporal) events could be said to affect it. Without the possibility of ascribing benefit or harm to such an entity, there is no way in which it could be said to possess a telos of its own. Such an entity would therefore lack intrinsic finality.
The implication of this is that a piece of computer software, even if it realised the properties of having a master program, nested organisation and embedded functionality, cannot be said to be alive, as its realisation is purely formal and not material. Hardware is an essential part of what it is to be alive. Living things are, after all, built from genes, not memes (pace Richard Dawkins).
(Some philosophers would argue that restricting the attribution of "life" to material entities is unduly narrow, as it would rule out the possibility of anything transcendent being alive - God, for instance. I do not propose to discuss this idea within my thesis, as my concern is with how the biological property of being alive is tied to the Aristotelian property of intrinsic finality and its attendant formal, material, efficient causal and temporal requirements. Aristotle himself employed a broader definition of life, which encompassed any kind of activity that could be regarded as having an intrinsic end - even a non-biological activities such as God's self-contemplation (Cameron, 2000, pp. 333-336.)
Spatial contiguity?
At this stage it might be asked whether an organism needs to be spatially contiguous. Could it have parts that were physically separated, but which were able to communicate with each other by transmitting chemical or electromagnetic signals? The idea is not a new one, as Holldobler and Wilson write:
The idea - the dream - of the superorganism was extremely popular in the early part of this [20th] century. William Morton Smith, like many of his contemporaries, returned to it repeatedly in his writings. In his celebrated essay, 'The Ant Colony as an Organism', he stated that the animal colony is really an organism and not merely an analog of one. It behaves, he said, as a unit. It possesses distinctive properties of size, behavior, and oragnization that are transmitted from one generation to the next. The queen is the reproductive organ, the workers the supporting brain, heart, gut, and other tissues. The exchange of liquid food among the colony members is the equivalent of the circulation of blood and lymph (1994, p. 110, italics mine).
Ants communicate with each other chemically, via pheromones, so the unity of the colony is maintained. The question of whether an ant colony is really one organism will be discussed in a later chapter, but the illustration has a point. There seems to be nothing inherently impossible in the idea of a spatially discontiguous organism. The conceivability of such an organism, however, in no way guarantees its real possibility. Moreover, there are two problems with the idea that need to be addressed: first, in what sense could a disconnected organism be described as one (the "unity" problem), and second, how could two such organisms be distinguished from one another (the "individuation" problem)?
I would suggest that the solution to both problems lies in Aristotle's notions of formal and final causation, recast as a master program with a nested hierarchy of dedicated functionality, possessing embedded functionality. I would propose that if:
(i) the parts of a superorganism, although physically separated, are controlled by the same master program, so that they are guaranteed to work together for the good of the whole;(ii) there is a nested hierarchy of functionality;
(iii) the repertoire of the parts' functionality is dedicated to supporting the functionality of the whole to which they belong; and
(iv) none of these parts is capable of surviving on its own,
then there is no real reason to ascribe the parts a separate telos of their own, as their ends are completely subsumed within that of the extended organism to which they belong. The above conditions are, I believe, sufficient for the existence of a superorganism, and the first three conditions are certainly necessary.
It needs to be stressed that the parts of a superorganism would need to be directed by a master program. Mere co-operation between distinct organisms, as is seen for example in symbiosis, does not suffice to make a superorganism. For example, some insects that feed on plants give sugary secretions to ants for food, and in return they are protected from enemies and sometimes even accepted as virtual members of the colony - a variety of symbiosis known as trophobiosis (Holldobler and Wilson, 1994, p. 143). Nevertheless, the behaviour of the adopted insects, as far as I am aware, is not chemically regulated by the colony which adopts them, so the insects cannot be said to be directed by a master program.
There are, to be sure, some cases of symbiosis where the degree of co-operation is far closer: the host organism acquires new genes from the symbiont by a process of lateral transfer, and the symbiont becomes so integrated into the host that it is effectively a part of the host cell (an organelle). In such cases, a genuinely new organism emerges, but as the parts are spatially contiguous (one is subsumed within the other), it cannot technically be described as a superorganism, where the parts are physically separated.
The "unity" and "individuation" problems can now be addressed. The unity of the superorganism is guaranteed by its master program, which controls all the parts. Two superorganisms are individuated by their possession of different master programs. To return to the ant colony analogy: each colony has its own distinctive pheromones, by which it discriminates between nestmates and strangers. Within a colony, pheromones comprehensively regulate the activities of the colony: they are used to signal the presence of food, recruit help when an ant is in danger, identify other castes, inhibit the laying of eggs by the queen's daughters, and fix the percentage of larvae that grow up to be soldiers - all for the benefit of the colony (Holldobler and Wilson, 1994, p. 55).
The idea that a superorganismic animal could have parts that functioned in different locations may seem counter-intuitive, but Varner has suggested a helpful analogy:
[S]uppose that, instead of being connected to my brain by long networks of nerves, the muscles in my hands were operated by a kind of natural radio signal. Then I could detach my arms and go down the hall to check my mailbox without leaving off typing (assuming, of course, that I could remove my arms without bleeding to death and that I am a touch typist!) (1998, p. 75).
Varner proposes a very inclusive criterion for individuation in asexually reproducing organisms: he suggests that "clonal reproduction never results in more than one individual, it just results in the one individual having noncontiguous parts" (1998, p. 74). He cites the example of an aspen grove, whose trees, although they appear distinct, are actually connected by the roots, underground. The grove is certainly one tree, and it is fundamentally no different from a live oak that splits into several branches just above the ground (p. 75). Next, he argues that if we sever the connections between the roots below the ground, we still have one tree, and finally, he avers that even if we remove one of the severed "parts" and plant it far away, it makes no ontological difference. I find this example unpersuasive. For my part, I can see no reason to call the removed tree (as I prefer to call it) a part of a larger whole, if its behaviour is no longer regulated by the whole to which it formerly belonged, and if it can survive and thrive without the whole.
Lower-level formal conditions for life
Possession of a boundary
What sort of concrete material realisation does a body need in order to qualify as being alive? Nicholas Humphrey (1993, p. 194) ties the possibility of consciousness to the possession of an intrinsic boundary by an individual. Without such a boundary, argues Humphrey, it could not feel anything happening to it and hence would have nothing to be conscious of. I would go further and suggest that nothing can be said to be alive without an intrinsic boundary.
Compartmentalisation, or the existence of an intrinsic boundary is Koshland's third "pillar of life". There are two reasons why having a boundary is important. First, an organism that lacked a boundary could not distinguish itself from other individuals, and would thereby be rendered incapable of advancing or defending its own intrinsic ends. For instance, it could not "defend itself against injury" (Koshland, 2002, p. 2215). Second, an organism needs a boundary to contain whatever parts and systems it needs to maintain itself. Koshland spells out the rationale in detail:
All the organisms that we consider living are confined to a limited volume, surrounded by a surface that we call a membrane or skin that keeps the ingredients in a defined volume and keeps deleterious chemicals - toxic or diluting - on the outside. Moreover, as organisms become large, they are divided into smaller compartments, which we call cells (or organs, that is, groups of cells), in order to centralize and specialize certain functions within the larger organism. The reason for compartmentalization is that life depends on the reaction kinetics of its ingredients, the substrates and catalysts (enzymes) of the living system. Those kinetics depend on the concentrations of the ingredients. Simple dilution of the contents of a cell kills it because of the decrease in concentration of the contents, even though all the chemicals remain as active as before dilution. So a container is essential to maintain the concentrations and arrangement of the interior of the living organism and to provide protection from the outside (2002, pp. 2215-2216).
While endorsing the thrust of Koshland's arguments, I should point out that he is assuming that living things are held together by chemical reactions. I would urge caution here: we cannot exclude the possibility that there may be an organism whose internal organisation is maintained by the transmission of, say, electromagnetic signals between its components. Such an organism could survive as long as its parts were suitably configured for sending and receiving signals. Indeed, in different environments, the organism might change its underlying hardware completely, taking in all kinds of "nutrients" whose sole common property was that they were suitable for being configured into the electrical circuitry required to maintain the organism. Tipler's (1982)example of the von Neumann probe, described in section 1.3.6 above, could operate in such a fashion, as it would be capable of taking in raw materials from the planet it landed on, and replicating itself. If such a machine could be constructed in such a way that its parts had internal relations, a nested hierarchy of organisation and dedicated functionality (i.e. all the requirements for intrinsic finality) then it could have multiple chemical "realisations", but would still qualify as being alive. However, even an organism constructed in this way would still need an internal boundary of some sort, to protect itself from the elements and to contain its vital circuitry.
The boundary condition rules out certain speculative proposals for what kinds of things could be described as organisms. For instance, gas clouds and light beams lack boundaries and therefore cannot qualify as organisms.
Seclusion
Koshland's seventh pillar, seclusion, or some way of preventing one set of chemical reactions from interfering with another, within a cell, is guaranteed in terrestrial organisms by specific enzymes that work only on the molecules for which they were designed. One might think that only a cellular life-form or an organism that was based on specific chemicals would have such a need, but Koshland offers an analogy which could equally apply to hypothetical organisms (discussed above) whose parts communicated by electromagnetic rather than chemical signals. He likens seclusion to insulating an electrically conducting wire so that it is not short-circuited by contact with another wire. The gist of the argument seems to be that organisms, having a large number of parts and an even larger number of interactions, require a certain degree of regulation to ensure that the interactions work properly - or, in Aristotelian terms, to ensure that organisms can achieve their intrinsic ends. The precise workings of this internal regulation would depend on the formal properties of the organism.
Cellular structure?
So far, the only terrestrial organisms we have examined have been cellular life-forms. Opinion is divided on whether acellular life-forms such as viruses should be considered to be alive. I discuss this question below. I conclude that despite the inadequate rationale ("They reproduce") offered by most scientists who believe that viruses are true life forms, there are sound Aristotelian reasons for viewing them as bona fide organisms. They appear to satisfy the formal, final and material requirements for being alive, as well as instantiating most of Koshland's "seven pillars of life". I also argue that although a virus is a life-form, it is only alive in a secondary sense of the word: it participates in the life of its host, to use a Platonic metaphor.
Opinion is divided on whether acellular life-forms such as viruses should be considered to be alive. On the account that I have defended, certain arguments against viruses being alive - the fact that viruses do not respire, display irritability, move, grow or excrete - are irrelevant, as these features are not constitutive of life as such. However, if one looks at the arguments advanced by defenders of the status of viruses, they tend to focus on viruses' ability to replicate, which, I have argued, is at most a necessary criterion for life, not a sufficient one.
Edward Rybicki, a professor of virology (University of Cape Town, 1998) rejects traditional textbook definitions of life, based on what he refers to as the "classical" properties of living organisms: reproduction, nutrition, respiration, irritability, movement, growth and excretion). He objects that such definitions are biased in favour of animals and plants, and argues that "the only real criterion for life is: [t]he ability to replicate".
Rybicki quotes two definitions of life to justify his characterisation of viruses as living things:
An organism is the unit element of a continuous lineage with an individual evolutionary history (Quoted by Rybicki from Luria S. E., Darnell J. E., Baltimore D. and Campbell A. 1978. General Virology, 3rd Edn. New York: John Wiley & Sons. p.4).
In other words,
an organism is merely the current slice in a continuous lineage; the individual evolutionary history denotes the independence of the organism over time (Rybicki, 1998).
According to this definition, viruses qualify as alive because they replicate, have an evolutionary history and do not depend on any particular host (or even species of host) in order to replicate. However, by the same token, a computer virus would also qualify as being alive.
Another definition, quoted by Rybicki, suggests that viruses are temporally non-contiguous organisms, which are alive when their inbuilt program, contained within their nucleic acid, is activated, and dead while the program is inactive:
Life can be viewed as a complex set of processes resulting from the actuation of the instructions encoded in nucleic acids. In the nucleic acid of living cells these are actuated all the time; in contrast, in a virus they are actuated only when the viral nucleic acid, upon entering a host cell, causes the synthesis of virus-specific proteins. Viruses are thus alive when they replicate in cells, while outside cells viral particles are metabolically inert and are no more alive than fragments of DNA (quoted by Rybicki from Dulbecco R. and Ginsberg H.S. 1980. Virology, pp.854-855).
This definition sharpens the rationale for regarding a virus as a living organism: a virus possesses a program of sorts, which is activated when it invades a host. This sounds like Aristotle's formal cause. A virus may even be said to be "designed" in a way to enable it to easily penetrate its host, take over the host cells and force them to make more copies of itself - in other words, it appears to possess intrinsic finality. In addition, a virus, unlike its computer analogue, possesses a material substrate: the nucleic acid strand of which it is composed.
It may be objected that the simple structure of a virus precludes it from possessing a nested hierarchy of organisation, one of the defining properties of living things. However, from the following description by Spencer, Nibert and Sgro (1994), it would appear that the proteins enclosing the nucleic acid in a virus interact in a co-ordinated fashion to promote the well-being and replication of the "whole" to which they belong:
A virus is a submicroscopic parasite that must infect a host cell in order to replicate, i.e. make copies of itself. The genetic information - the viral genome - is encoded by nucleic acid, either DNA or RNA. The genome is enclosed in one or more layers of protein and, if the virus is enveloped, lipid as well. In many cases, the protein layers are highly symmetrical and are composed of many copies of a few viral proteins, arranged in shells or "capsids," in which repetitious protein-protein interactions are found....
Each virus encodes its own collection of viral proteins, acting in concert, each with specific roles that enable or enhance viral replication. The function of each viral protein is inherent in its tertiary structure (three-dimensional conformation). Some viral proteins function as components of the virus capsid. Others act as enzyme catalysts of chemical reactions that are essential to viral replication, such as RNA synthesis or proteolysis. Some viral proteins may actually do both, participating in forming the capsid and acting as an enzyme catalyst (italics mine).
From the foregoing description, it seems unreasonable to deny that viruses are genuinely alive, as they appear to satisfy the formal, final and material requirements for being alive, as well as instantiating most of Koshland's seven pillars: a program (DNA or RNA), improvisation (they mutate), compartmentalisation (a coating), energy (supplied by the host cell), regeneration (they reproduce), and adaptability (they can hide inside their host until conditions become more favourable). (The satisfaction of the seclusion criterion is more doubtful.) Despite the inadequate rationale ("They reproduce") offered by most people who believe that viruses are true life forms, there are sound Aristotelian reasons for viewing them as bona fide organisms, unlike, say, computer viruses.
This does not mean that we can put viruses on a par with other living things. The life they have is a borrowed one, as they rely on their host to provide all of their metabolic functions and raw materials:
Without a host cell, viruses cannot carry out their life-sustaining functions or reproduce. They cannot synthesize proteins, because they lack ribosomes and must use the ribosomes of their host cells to translate viral messenger RNA into viral proteins. Viruses cannot generate or store energy in the form of adenosine triphosphate (ATP), but have to derive their energy, and all other metabolic functions, from the host cell. They also parasitize the cell for basic building materials, such as amino acids, nucleotides, and lipids (fats) (Davidson, M. and Florida State University, 2002).
Using Platonic terminology, we may say that a virus participates in the life of its host, in which it "lives, and moves and has its being" (Acts 17:28, originally from Epimenides' poem, Cretica, in honour of Zeus). In other words, a virus is a life-form, but only in a secondary sense of the word.
Some viruses, according to Rybicki (1998), are associated with satellite viruses: for instance, the tobacco necrosis satellite virus, which depends for its replication on the presence of the tobacco necrosis virus. These satellite viruses could be described as "third-tier" or tertiary life-forms.
Efficient causal conditions for life
Metabolism
The extraction of chemical energy from nutrients, or metabolism is Sarver's (1999) fifth condition for life. As we have seen, viruses do not metabolise: they derive their energy, and all other metabolic functions, from their host cell. However, this arrangement only serves to highlight the fact that life on earth would not possible without the extraction by some organisms of chemical energy from nutrients. However, it would be unwise to exclude the possibility of a form of life elsewhere in the universe which did not require chemical energy but was able to use some other form of energy.
There is, however, a more fundamental reason for regarding some form of metabolism as a necessary feature of life. As we saw in section 1.3.1, the biological property of nutrition, defined as an organism's "ability to take disorganized material and spontaneously organize it" into its own structure (Wolfram, 2002, p. 824), can be regarded as not only an efficient causal condition for life, but also a thermodynamic condition, insofar as the exercise of this function results in a local entropy decrease. Because the laws of thermodynamics apply everywhere in the cosmos, we can assume that no life-form could thrive anywhere without the ability to incorporate new material into itself.
Interaction with the environment
Interaction with the environment is Sarver's (1999) seventh condition for life. Since it is a law of nature that the entropy of any closed system increases over time, the conclusion that living things necessarily require energy to combat entropy seems inescapable. To obtain this energy, they must therefore interact with their surroundings. Without this interaction, any organism would rapidly perish and be unable to realise any of its intrinsic ends.
Ecology can be defined as the study of the interaction between organisms and their environment.
Independence
According to Winder's (1993) definition of life, a living thing must be able to live independently of other organisms. This requirement appears empirically dubious: there are some forms of symbiosis and parasitism in which one organism is heavily dependent upon another. However, Winder might argue that the dependent organism could always find another host, and therefore does not need the one in which it currently resides.
Animal embryos constitute another exception to Winder's requirement. Winder might reply that an embryo can be viewed as part of its mother. But according to each of the three formal conditions I have developed for being alive listed above, an animal embryo, although totally dependent on its mother, has to be considered as a distinct organism, since it possesses its own master program, nested hierarchy of organisation and embedded functionality, giving it a telos of its own, which may at times even conflict with that of its mother (e.g. when it competes with its mother's body for access to nutrients). (An animal embryo is a "self-assembling" organism, in the sense that although it cannot develop properly outside its mother's body, it already possesses a complete internal program for putting itself together. No extra "assembly instructions" are required once it has inherited its full complement of genetic material from its parents.)
From a philosophical perspective, even the notion that an entity A might have a good of its own, while remaining depdendent throughout its life on another entity B for its subsistence, appears to make perfect sense. The worry that A's ends would be wholly subsumed within B's is misplaced: this would occur only if A's functionality were dedicated to supporting that of B, in the way described in section 1.4.2. In any case, competition between A and B for access for resources (food or oxygen) would suffice to establish a disparity between A's and B's ends.
I conclude that there are no good reasons for regarding independence as a necessary feature of life.
Temporal conditions for life
Temporal contiguity?
Perhaps the most fundamental question relating to the temporal conditions for life is whether an organism needs to be temporally contiguous. Could there be an organism which lived for an interval of time, only to have its life stopped and subsequently re-started again when conditions were favourable? The answer appears to be in the affirmative. Close approximations can be found in the real world - for instance, bacterial spores, a resting phase displayed by some types of bacteria in response to adverse environmental conditions. Certainly, philosophical problems of identity would arise if the organism were to completely disintegrate and subsequently be re-constituted. In that case, it could be argued that it was no longer the same organism. However, if the information that constitutes the organism's "formal cause" is preserved within the "body" (or "matter") of the organism, even while its life-functions have ceased, then the issue of identity over time becomes fairly unproblematic. In Aristotelian terms, what seems to be required for identity is that the form be preserved over time within the organism's matter, even when every organismic function (ergon) has been switched off.
Thermodynamic requirements: energy, reproduction and a life cycle
The fourth and fifth "pillars of life" listed by Koshland (2002, pp. 2215-2216) are energy (to keep living systems metabolising) and regeneration (including reproduction) to compensate for wear and tear on the system. Since the intrinsic end or "purpose" of these features is to hold back the inexorable march of time, they may be considered as temporal conditions for life - more specifically, as thermodynamic requirements.
As Wolfram (2002, pp. 824, 1178) correctly observes, these conditions are not unique to living things. The question we have to address is: are they necessary conditions for life? Given that all living things require some degree of functionality in order to achieve their intrinsic ends, Koshland's energy requirement - that a living thing must be a thermodynamically open system - seems indispensable, given the laws of nature which obtain in our universe. The physical necessity of regeneration (given the laws of thermodynamics) also seems inescapable, to counter what Koshland calls the thermodynamic losses of a metabolising system.
Although he classifies it as an aspect of regeneration, Koshland also considers reproduction to be a necessary feature of living systems. (As we saw earlier, reproduction cannot serve as a sufficient condition to define life, as it is found in a host of systems, including abstract computational systems, that "bear no other resemblance to ordinary living systems" (Wolfram, 2002, p. 824).)
Koshland is careful to point out that the capacity to reproduce cannot be considered a defining property of living individuals (for then, as he remarks, two rabbits - a male and a female - would be alive but one, by itself, would be dead), but argues that reproduction is a necessity for any kind of living system, for thermodynamic reasons. According to Koshland, reproduction is necessary to counter the accumulation of slight imperfections in the constant resynthesis of bodily constituents during an individual's lifetime (in other words, ageing). Reproduction gives a living system the opportunity to start over.
One might object that for all we know, there might be some open system on some planet that is capable of regenerating itself almost perfectly, over a very long period of time - say, a million or a billion years. Such a system might exhibit the finality, form and functionality of a living individual, even without the capacity to reproduce - and then, just die out. But this objection begs the question of how and whether such a system could arise in the first place.
Moreover, there are two other weighty reasons for considering reproduction seriously as a necessary feature of life. The first is the fact that every kind of living thing with which we are familiar, reproduces. As Aristotle remarks (De Anima 2.4, 415a28-29):
For this is the most natural of the functions of such living creatures as are complete and not mutilated and do not have spontaneous generation, namely to make another living thing like themselves, an animal an animal, a plant a plant ... (1986, p. 165).
Leaving aside Aristotle's quaint belief in spontaneous generation, his point remains valid. Reproduction is found in every species of living thing on earth. In Aristotelian terminology, we might say that an organism's capacity for reproduction is a "proper accident" of its soul - a necessary by-product of the more fundamental property of being alive. (However, Aristotle (De Anima 2.4, 415a24-25) also classifies nutrition as a function of the "first and most general faculty of the soul, in virtue of which all creatures have life" (1986, p. 165). We therefore have to consider at least the theoretical possibility that there may exist some life-form possessing the faculty of nutrition without reproduction.)
The second reason for regarding the ability to reproduce as a hallmark of life is the Darwinian or historical paradigm of biology: living things cannot be considered apart from their genes, and the reason why living things have the genes that they possess is that those genes have out-competed other genes in a four billion-year evolutionary race to replicate themselves. If all life-forms are the product of natural selection, then reproduction is an essential characteristic of all species. (I say "species" rather than individuals, because in many species, there are biologically normal individuals whose morphological type - which I shall discuss in section 1.4.7 - renders them incapable of reproducing.)
It should, however, be borne in mind that we know of only one planet so far which supports life, so it seems unwise to generalise about any life-forms on other planets. In the meantime, we cannot dispense with reproduction as a necessary condition of life until we discover some mechanism whereby a life-form could originate on a planet, without some process of self-replication being involved. (Interestingly, a new theory by Martin and Russell (2003) suggests that cells, whose walls were originally made of iron sulphide deposited by hot springs, originated first and served as incubators for organic molecules, which eventually acquired the ability to self-replicate. In other words, the cell may be a more basic feature of life than reproduction.)
Sarver's (1999) sixth defining feature of life is the occurrence of characteristic phases of development in a life cycle. A life cycle of some sort seems unavoidable if we accept that reproduction is a necessary feature of life. Another reason for regarding a life cycle as a sine qua non of life in our universe is the fact that living things inevitably age and wear down.
Evolutionary requirements for life: ability to evolve
Koshland's second pillar, improvisation, or a way in which an organism can change its master program (achieved on Earth through mutation), appears to be a necessary condition for life in a universe where environmental change is the norm. Without such a mechanism, Koshland argues, species would rapidly die out. It would of course be a mistake to say that evolutionary change occurs "for the sake of" the species; Darwinian evolution is a random process which does not occur "for the sake of" anything. We may, however, legitimately say that a capacity to evolve enables lineages to survive: without it, they would soon perish.
This leaves open the question of whether non-evolving life might have originated on some other planet and rapidly died out - perhaps because its replication mechanisms were too perfect to allow for the occasional genetic copying error. There is, however, another reason for regarding the ability to evolve as a necessary feature of any life-forms that emerge through natural processes. The high degree of organisation of even the simplest organism makes its emergence by purely random processes (i.e. molecules fortuitously coalescing together) vanishingly improbable. The only natural alternative is a non-random one, and the most obvious candidate is the non-random winnowing mechanism of natural selection. In other words, some kind of (abiotic) chemical evolution, constrained by natural selection, generated the first structures that fulfilled all the criteria for being "alive". (Another possibility is that there are as-yet-unknown laws of the universe which account for the emergence and self-organising properties of life (Kauffman, 1993, 2000).)
But even if life can only emerge naturally as a result of natural selection, there seems to be nothing to prevent human beings from manufacturing artificial life-forms that possess the vital property of intrinsic finality (and the attendant formal properties), but lack the capacity to evolve. On my account, these structures would have to be considered alive.
Even if the capacity to evolve should prove to be a necessary temporal feature of life in our cosmos, but its necessity would only be knowable a posteriori. It would therefore be very unwise to build the concept of evolution into the very definition of life.
Adaptability
Koshland's sixth pillar (behavioural adaptability to environmental hazards) seems unexceptionable, if rather vague. Koshland elaborates:
behavioral manifestations of adaptability are a development of feedback and feedforward responses at the molecular level and are responses of living systems that allow survival in quickly changing environments (2002, p. 2216).
The obvious qualification is that adaptability, like rapidity of environmental change, is a matter of degree. Some organisms live in very stable environments; others, like ourselves, are in a continual process of adjustment.
1.4.7 What does it mean for a living thing to have a nature?
The Darwinian and Aristotelian conceptions of life are usually thought of as diammetrically opposed. In particular, Aristotle's doctrine that every species is eternal and that its members share a common nature is widely regarded as utterly antithetical to Darwin's theory that species are in continual flux and evolve over time. I shall argue that on the contrary, the Aristotelian and Darwinian accounts of life have much in common, and that although Aristotle's definition of a species is in need of some revision, a neo-Darwinian concept of nature remains viable.
A central feature of Aristotle's account of nature was his observation (Parts of Animals i.1 640a25-6, 640b1-4, ii.1 646a35; Generation of Animals iv.3 767b35; Physics ii.1 193b8, ii.2 194b13, ii.7 198a25; Metaphysics vii.7 1032a22, xii.3 1070a29, xii.5 1071a20, 1071a25, xiii.10 1087a21) that living things normally beget other living things after their own kind - or, as Cameron (2000, p. 106) puts it, "breed true". This fact alone was sufficient to convince him that the opinion of his philosophical opponent Empedocles, that everything which happens to plants and animals is due to chance, could not possibly be correct. Empedocles' account has been described as proto-evolutionary: he claimed that new life-forms fortuitously appear (and old ones disappear) over the course of time. However, Aristotle argued that Empedocles' biological theories were utterly unable to account for the simple fact that creatures breed true. Chance, by definition, cannot account for regular and reliable occurrences in nature - such as the fact that creatures breed true. If living things breed true, Aristotle maintained, it must be because they are the sorts of things they are. As Cameron succinctly puts it:
[T]he fact that species breed true can only be explained by postulating animal and plant natures. Nature, not chance, is the cause of breeding true (2000, p. 107).
It may surprise some readers to realise that Darwinists come down on Aristotle's side of this ancient philosophical stoush. Although Darwin taught that species evolve over time, what is usually overlooked is the glacial pace at which they do so. The average lifespan of a species is measured in millions of years. Novel variations arising within a new generation are a rarity. That being so, parents require some natural mechanism for propagating their genetic traits to their offspring. Many of the definitions of life listed above specifically mention this point. (Thus Monod (1971) includes reproductive invariance as a characteristic of life: the source of information expressed in a living organism is another structurally identical object, whose information corresponds to its own structure. Maynard Smith, 1975, mentions heredity as a characteristic of life; Winder's 1993 definition mentions "self-replication with each offspring slightly different" (italics mine); Sarver, 1999, stresses that reproduction "enables the transmission of traits from parents to offspring".)
(Aristotle's true "polar opposite" in modern times would have to be Richard Goldschmidt, who proposed that living things do not always reproduce after their kind: on very rare occasions, "hopeful monsters" are born which are radically different from their parents, enabling new biological functions to arise in nature. Darwin maintained the contrary view that if nature is capable of generating complex structures in organisms, then they must arise gradually. The sudden appearance of such structures would be a miracle; hence Darwin's invocation of the old aphorism that "Nature does not make leaps".)
The real difference between Aristotle and modern Darwinists lies not in the latter's supposed denial of the objective reality of species, but in their differing conception of a species. Plato and Aristotle employed a typological or morphological concept:
The word 'species' conveyed the idea of a class of objects, members of whom shared certain defining properties... Such a class is constant, it does not change in time, all deviations from the definitions of that class are merely "accidents", that is, imperfect manifestations of the essence (Mayr, 1996, p. 267).
The biological concept of a species is quite different. The term "species" may refer to either a category in the Linnaean hierarchy (kingdom, phylum, class, order, family, genus, species) or to a taxon - "Species are groups of interbreeding natural populations that are reproductively isolated from other such groups" (Mayr, 1996, p. 264). The biological purpose of the species is "the protection of a harmonious gene pool" (Mayr, 1996, p. 264). Reproductive isolation is achieved through isolating mechanisms within individuals. Isolating mechanisms are not 100% efficient; thus related species may sometimes hybridize. Nevertheless, "hybrids between species, particularly animals, are almost always of inferior viability and more extreme hybrids are usually even sterile" - although occasionally in plants they may give rise to new species (Mayr, 1996, p. 263). The biological species concept is only applicable to organisms that reproduce sexually; it does not apply to asexual organisms.
Historically, the reason why scientists began to abandon the morphological conception of species in the second half of the nineteenth century was that morphological characters proved unreliable for the recognition of biological species: members of closely related sibling species may have few or no morphological differences, while numerous different morphological types may occur within a biological species, either because of individual genetic variation or different life history categories (males, females, immatures) (Mayr, 1996, p. 268).
I would suggest that the modern biological concept of a species, far from being at odds with Aristotle's philosophy, actually provides a better explanation for Aristotle's observation that living things "breed true": on the modern concept, this is true by definition. That does not, however, make it trivial: the fact that all populations of organisms do in fact breed true remains an a posteriori truth, which is grounded in the nature of each species of organism. I shall say more about these natures below.
Mayr (1996) describes biological species taxa as concrete phenomena: he even describes them as "particulars, 'individuals', biopopulations". This brings us to the most significant difference between the traditional morphological and modern biological concepts of a species: according to the former way of thinking, an individual is a member of a species by virtue of its own characteristics; whereas on the latter view, the relevant characteristics are those of the population as a whole, which is said to comprise a gene pool. An individual is said to belong to a species - even if it is sterile or denied the opportunity to interbreed with other individuals -if its genes are the product of the same gene pool as that of the population.
Aristotle described three major holistic ends of an organism:
individual flourishing (Physics ii.2 194a28-33, ii.3 195a23-5, ii.7 198b8-9; Politics i.2 1252b34-5; Eudemian Ethics i.8 1218b9-11, ii.1 1219a9-11; Metaphysics i.3 983a31-2);maturation (Generation of Animals ii.3 736b4-5; Physics ii.2 194a29-33; Movement of Animals 6 700b15-16); and
reproduction (Politics i.2 1252a28-30, De Anima ii.4 416b23-5, Generation of Animals ii.23 731a25-b7, History of Animals viii.1 588b25-6).
It is clear that individual members of the same species do not share identical ends: the two sexes, for instance, possess different internal organs, so their individual flourishing is realised differently. Different morphological types within the same species also have different ends.
On the other hand, if we look at the holistic ends that are realised by all of the various members of a population as a whole, it becomes readily apparent that these ends remain stable within a population over long periods of time. For any individual organism X we select from any biological population, there are individuals (of the same sex and morphological type) among its ancestors thousands of years ago, whose organs possess the same ensemble of functionality as those of X; thus the individual flourishing (on a purely biological level) of the organism X is the same as that of its ancestors. Additionally, X's biological body clocks will be the same as those of its "near" ancestors who lived "only" a few thousand years ago, meaning that the goal or end point of its process of maturation is the same. Finally, the individual X belongs to a gene pool which is sufficiently stable, even over a period of thousands of years, that any accumulated changes in the population's gene pool will not yet be sufficient to constitute a reproductive barrier; thus X's reproductive ends are the same as those of its ancestors. This suggests one way in which a neo-Aristotelian who accepts Darwinism might build the concept of "nature" into the definition of a chronospecies - a biological term for the temporal extension of a species.
If for any individual X selected from a population at time t2, some ancestral individuals can be found in the same population at an earlier time t1, such that:
(i) the part-whole functionality of their organs (and hence their bodily morphology) matches that of their descendant X;(ii) the end points of their biological body clocks are the same as those of their descendant X; and
(iii) there are no reproductive barriers such as would affect viability of offspring if - counterfactually - these ancestors were to mate with their descendant X,
then we can say that:
(a) these ancestral individuals have the same holistic ends as their descendant X;(b) the nature of the population has remained the same over the time interval from t1 to t2; and therefore
(c) the population at t1 belongs to the same chronospecies as the population at t2.
Standard definitions of "chronospecies" contain an ineliminable reference to counterfactuals, as my proposed definition does. The difference between my definition and standard definitions lies in the explicit reference to ends, and the fact that species identity is made consequent upon the fact that for any individual selected from a population, some of its ancestors possess the same ends and hence the same nature.
(For instance, Hyperdictionary (2003, Web address http://www.hyperdictionary.com/dictionary/chronospecies) defines a chronospecies as follows: A chronospecies is a species which changes physically, morphologically, genetically and/or behaviourally over time on an evolutionary scale (experiences a phyletic shift) such that the species from the early point in time and the species it becomes at the later point in time could not be classified as the same species had they existed at the same point in time.)
Cameron has argued persuasively (2000, pp. 138-166) that Aristotle regarded the property of directedness upon an object as an ontological primitive. That being the case, Aristotle's view might appear to be in conflict with the Darwinian tenet that evolutionary processes in nature are "blind" and not "directed" at anything. However, I would suggest that the contradiction is only apparent: the randomness of evolutionary processes is quite compatible with the occurrence of non-random teleonomic processes within the body of an individual organism. If evolution had an end, it could only be extrinsic - a notion which Darwinism rejects - whereas the ends of an individual organism are intrinsic. The fact that evolution has no extrinsic "goal" or "purpose" does not mean that an individual's body parts possess no functions or intrinsic ends.
The final obstacle for a neo-Aristotelian account of nature relates to transitivity of identity. An individual X may have the same nature (according to the teleological criteria listed above) as its ancestors Y1, Y2, ... Ym, and these individuals may have the same nature as their ancestors Z1, Z2, ... Zn, yet it may be the case that X and Z1, Z2, ... Zn possess different natures by the same criteria (e.g. due to the accumulation of genetic reproductive barriers over a long period of time) - generating a paradox.
The correct resolution of this paradox is to recognise that the notion of "sameness" used here differs from most standard cases. First, there is no external yardstick with which we can measure the feature being compared between individuals: an individual's species, like its neighbourhood, can only be defined relative to the individual itself. In this respect, an individual's species is unlike its color (which can be measured on a scale of wavelengths and intensities) or the number of hairs on its head. Hence the comparative property of "belonging to the same species as an individual X" can only be defined relative to X, like the property of "being in the same neighbourhood as X".
Second, a species is an inherently imprecise concept because the notion of a reproductive barrier is imprecise. This fact makes it impossible for scientists to fix precise boundaries for species. The reason for the absence of reproductive barriers between an individual and its proximate ancestors is that the genetic changes that have accumulated in the population since these ancestors died are as yet too tiny to constitute a barrier: viewed against the variability of the gene pool as a whole, they could be described as background "noise". Likewise, new functions are evolving in populations all the time, but because it takes millions of years for a new function to evolve, the appearance of incipient functions is not noticeable over relatively short intervals of thousands of years. Only after a very large number of generations have elapsed can we speak of a change of nature in the population. In Aristotelian terms, we can say that the intrinsic ends of a lineage of organisms change over very long periods of time.
There are thus two good reasons why transitivity of the sameness relation might not hold. The exact point at which a lineage changes its nature and evolves into a new species may elude us, but this generates transitivity paradoxes only if we assume that "nature" is both an externally defined concept and a precisely defined concept. In any case, the fact that species sameness is not a transitive relation should not occasion any perplexity. The sceptical query, "Where do you draw the line between a species and the species that succeeds it?" presupposes that a clear line has to be drawn in the first place.
Likewise, the fact that two distinct species S1 and S2 could both conceivably share the same nature as the common ancestral population from which they both arose, does not vitiate the concept of nature as such. Indeed, the very question, "Which species does the ancestral population belong to - S1 or S2?", is anachronistic: at the earlier time t1, it cannot be meaningfully posed. What we should say here is that small differences within two recently segregated populations which do not yet constitute a reproductive barrier may, over the course of time, accumulate to the point where the two populations no longer possess the same nature.
I conclude that the concept of nature, while needing considerable revision in the light of what scientists now know about evolution of new species, remains a viable and useful one, as it situates an individual within a community where there are no reproductive barriers between members, and where some other individuals can be found who share the same teleological ends.
1.4.8. Do living things have a privileged ethical status?
Problems with the desire-centred theory of welfare
The notion that a non-sentient organism (a plant, let us say) could be said to have interests sounds strange to many philosophers. Feinberg (1974, pp. 49-50) has argued that only a being with conations (e.g. wishes, desires, hopes, drives, aims and goals) can have interests, and that only conscious conations can define interests. Varner (1998, pp. 57-61) criticises this view because it does not do a good job in accounting for cases where an individual's desires and interests conflict.
Firstly, an individual may have desires (or conscious conations) that go against his/her best interests. Varner asks us to imagine the case of Nanci, a cat who desires access to the outdoors, but does not and cannot understand the risks involved, such as contracting the feline leukemia virus (or, in the area where I live, being run over by a car). Nanci may want to go outside, even though it is manifestly obvious (to us) that her desire is against her best interests. While a biologically grounded theory of interests can readily explain why this is so (e.g. viruses are bad for her health), a theory which grounds interests solely in mental states requires awkward counterfactuals to support the same conclusion (e.g. if, per impossibile, she could master a language and understand what we do, she would no longer desire to go out).
Secondly, an individual may have interests that (owing to ignorance on his/her part) he/she does not desire. It was certainly in the interests of nineteenth century mariners to take 10 milligrams of ascorbic acid a day, to avoid scurvy, but because they knew nothing about ascorbic acid, they had no desire for it. Such a case is unproblematic if we allow interests to be grounded in biological facts, but a psychological, desire-based account of interests can only construe the mariners' interests counterfactually: the mariners would have desired ascorbic acid, had they been sufficiently informed (in other words, had they known what we now know).
The psycho-biological account of welfare
Varner proposes what he calls a
psycho-biological account of welfare, according to which to say X is in A's interest means that(1) A actually desires X, [or](2) A would desire X if A were sufficiently informed and impartial across phases of A's life, or
(3) X serves some biologically based need that A has in virtue of being the kind of organism A is (1998, p. 62).
Varner makes it clear that the "or" is meant to be inclusive. His account can easily explain the anomalous cases cited above, by reference to condition (3). The only significant criticism I would wish to make of Varner's account is that it does not prioritise desires, informed desires and biological needs. Surely, in the case of Nanci, if there is a feline leukemia epidemic, then going outside is not in her interests, even though she may take an interest in it (i.e. desire to go outside) - to cite a distinction that Varner himself makes (p. 57). On Varner's psycho-biological account, a strange conclusion follows: both going outside and staying indoors are in Nanci's interests: the former satisfies condition (1), while the latter satisfies condition (3). One might allow the co-occurrence of conflicting interests satisfying conditions (2) and (3) - for instance, it may be in a firefighter's interest to remain in a burning building in order to satisfy her impartial interest in saving as many lives as possible, while getting out as quickly as possible may serve some biological need of hers (especially if she is predisposed to getting bronchial problems) - but it seems unreasonable to put mere desires, especially uninformed ones, on a par with biological needs.
One merit of Varner's account is that it would allow us to say that plants have interests, as they can satisfy condition (3). However, the account is open to an obvious riposte: artifacts (e.g. cars and human-built computers) have needs too, so why do we preclude them from having interests? (Varner considers the idea that a can opener has interests to be a reductio ad absurdum.) First, he addresses the empirical question: how do the needs of plants (or more generally, organisms lacking desires) differ from those of artifacts?
Varner solves this problem by proposing an etiological account of life: he proposes that "biological functions, rather than goals or end-states" are required to "draw a sharp distinction between all artifacts, on the other hand, and all living organisms on the other" (1998, p. 67). According to Varner, what is good for an organism cannot be adequately defined in terms of its end-states, as artifacts (such as a Patriot missile) may also have "built-in goals". On Varner's account, the function of an organ or subsystem is explained in terms of the selective advantage it provided its owner's ancestors over other individuals lacking this function. I have already discussed the problems with Varner's etiological account of life in section 1.3.6, so I shall not repeat my criticisms here. Varner's claim that the Patriot missile has built-in goals was evaluated in section 1.4.5, where I argued that the missile lacked intrinsic finality.
Varner then argues that organisms, unlike artifacts, are the result of natural selection (1998, p. 69), from which it follows that (according to his etiological definition) biological functions are only found in organisms. Varner then re-writes condition (3) of his psycho-biological account of interests as follows:
(3) X would fulfill some biological function of some organ or subsystem of [an individual] A ["biological function" is then defined in terms of its selective advantage, as above] (1998, p. 68).
The fact that organs or subsystems have a function gives their possessors a "good of their own" in an objective, biological sense - a feature which artifacts lack:
Cars, can openers and intrinsically valuable things [e.g. works of art - V.T.] all can be coherently said to have needs, but only things with a good of their own can coherently be said to have interests (1998, p. 56, italics mine).
The problem with Varner's account is that it uses the concept of natural selection to make a sharp distinction between organisms and artifacts - a distinction which is both empirical and ethical. Although the property of having a hsitory of natural selection may track the organism-artifact distinction pretty well (if we choose to ignore the troubling cases of abstract computational systems that evolve, and future artifacts that may qualify as alive), it is incapable of defining it. To define this distinction, we require the concept of intrinsic finality, which is manifested in the formal properties of possessing internal relations, a master program, a nested hierarchy of organisation and dedicated functionality.
A more serious problem with Varner's distinction is that although provides us (in practice) with an excellent yardstick for objectively determining what is good for an organism, it does not properly define what "good" means. "Being the product of Darwinian evolution" does not appear to be a morally relevant property per se.
The concept of natural selection appears inadequate to explain why organisms, and not artifacts, "qualify ... for direct moral consideration" (1998, p. 69). The nub of Varner's argument (1998, pp. 73 - 74) is that (i) the fulfilment of biological functions in sentient organisms is in their interests irrespective of their even being able to take an interest in their fulfilment (as is shown by the cases of Nanci the cat, who wants to go out during an epidemic of feline leukemia virus, and the nineteenth century mariners, who had no desire for ascorbic acid); so (ii) the fulfilment of biological functions (which we can enumerate in a non-arbitrary fashion, using the concept of natural selection) in non-sentient organisms, should be considered as being in their interests, even though they cannot take an interest in their fulfilment. I do not wish to criticise the logic of Varner's move from (i) to (ii), which seems reasonable. I would simply like to point out that the role served by natural selection in this argument is merely to identify what the biological functions of organisms are, rather than why they are morally significant. That question is left unanswered.
Putting the problem another way: Varner has failed to answer the question of why a biological interest, per se, matters morally, while a mere need (e.g. a car's need for oil) does not. Granting that the needs of plants are the product of Darwinian evolution while the needs of cars are not, I might say, "So what?"
Outline of an alternative view
It has been argued that there is a real, non-arbitrary distinction between living and non-living entities, and that this difference can be explained in terms of the form and finality of living things. What is good for an organism can be ascertained from understanding the organism's master program, its hierarchy of organisation, and how its functionality, on each level, supports that of the next highest level.
We have seen that defining a thing's "good" as "the set of functions which helped its ancestors" does not suffice to make them morally relevant. But if instead "good" is defined (roughly) as "the set of functions to which its parts are dedicated", then at least its benefit to the thing itself is clear.
The next question to be addressed is: does this difference matter ethically for us? Is there something about being alive that warrants special ethical treatment?
I would like to offer answer this question by highlighting a deficiency in the desire-centred theory of welfare, which ignores purely biological interests. If this theory is correct, then "doing good" has to be cashed out in terms of "satisfying someone's desires" - perhaps, if one is generous, the greatest number of desires in the greatest number of interested parties, along the lines proposed by some utilitarians. Yet it is not at all clear why the satisfaction of anyone's desires is even a prima facie good thing, without further need of justification. While it is factually true most of the things people want are good for them, most of the time - otherwise they would probably be dead - this does not tell us why X's being wanted by A should make X good for A.
If instead we consider the satisfaction of biological interests, then in this context, "doing good" means (on my proposal) "promoting some biological function(s) in an organism, which its body parts are dedicated to supporting" - roughly, promoting its health. Promoting the health of an organism, as a doctor, a vet or the parent of a child might do, does sound like a good that needs no further justification. If this is not acting ethically, then it is difficult to see what might be.
Of course, the good of a moral agent - or even a sentient animal - is a multi-faceted thing, which certainly cannot be reduced to the notion of health. In chapter 5, I explore the notion of "basic goods" and argue that their scope encompasses not only the human arena but the entire spectrum of goods that can be realised by organisms in the world around us.