The argument from marginal (human) cases
Many animal liberationists employ what Dombrowski (1997) calls the argument from marginal cases to argue that there are no morally relevant differences between animals and human beings who are either very young, severely intellectually disabled or permanently comatose. Likewise, Regan (1988) defines "subjects-of-a-life" as mentally normal mammals aged one year or more.
On the other side, there is a long tradition of differentiating marginal human cases from other animals, on the basis of their future or past potential: i.e. because of what they will be (infants), could have been (people with severe mental disabilities), or once were (permanently comatose patients). It is also argued that we have ties of kinship to these human beings which justify our treating them as rights-bearers. "Actualists" counter that a potential X does not have the same rights as an actual X, and that sentimental considerations such as kinship should not over-ride moral principles.
I believe that we do both animals and so-called "marginal human cases" a disservice by assimilating the former to the latter. Instead of appreciating animals for the kind of organisms they are, we end up viewing them as second-rate people, while remaining oblivious to the genuine humanity of "marginal cases".
On the telos-based account of obligations which I am defending here, there is a vital difference between a newborn human baby and a newborn chimpanzee: the flourishing of the former, but not the latter, includes trying to lead a good life, as a moral agent. This alone justifies treating the two individuals differently. Killing the human baby would be an evil of a different order of magnitude than killing the chimpanzee. However, I readily concede that defenders of "marginal human cases" are wrong to base their case solely on the potential rather than the actual properties of these human beings.
I have argued that an organism's moral standing is grounded in its telos, which is defined by its nature. I have defined an individual's nature in terms of the genetic information which the individual must possess in order to exercise the entire range of basic goods that typify the species to which it belongs. (A given individual will inevitably possess a copy of this information that is slightly damaged by mutation, but the standard information required to encode each of its functions can be determined by examining the DNA of other individuals with whom it can inter-breed.) It is this information, encoded within each cell as an internal "master program", which regulates the development and structure of the organism and the interactions between its parts, and thus determines the telos of that species - i.e. what its flourishing consists of.
What makes human individuals different from other animals is the information that they have: an internal program (in their DNA) that contains instructions for their development into rational adults who care about the good life. This program is not potential but actual: it consists of a sequence of coded instructions, contained in these individuals' DNA. Additionally, the program is not dormant but actually executing: it controls our development and supports our bodily structure and functions, during every moment of our waking or sleeping lives.
The "marginal human cases" discussed by Dombrowski (1997) possess a complete, actually executing copy of this internal master program in every cell of their bodies. In infants, the only obstacle to its full expression is time; in intellectually disabled people, DNA damage that has corrupted a few of the program instructions; and in permanently comatose patients, bodily injury. It is this master program that determines what things are good for these human individuals to realise, even if they are precluded from doing so. What is good for us would be good for them, and vice versa, whereas what is good for a chimp would not necessarily be good for them. Since, as we have argued, their telos determines their moral status, they matter as much as we do.
Dombrowski (1997, p. 92) criticises the arguments of Holmes Rolston, who believes we should respect injured or damaged "marginal cases" on grounds of charity, for historical reasons:
We do not respect them for what they are but respect the full humans they were or might have been; we repair the tragedy by charity, rather than do strict justice to their condition (quoted in Dombrowski, 1997, p. 92).
Dombrowski (1997, p. 93) argues that we should respect these human beings, not for historical reasons, but because of what they are: sentient beings. It should be quite clear that my own position is different from Dombrowski's and Rolston's: I maintain that we should respect these human beings as our moral equals, not because of what they are or were or will be or might have been, but because of what they should be - in other words, because of their telos.
Just as we could envisage future medical advances enabling severely impaired "marginal animal cases" to attain sentience, we can realistically imagine some of these "marginal human cases" becoming human moral agents, thanks to the same medical advances, without altering either their physical identity as individuals or changing their nature as human beings. In all these cases, the uniquely human instructions that code for the possibility of rational agency are already there within the individual's body cells. I suggest that since these are what make humans special, any individual possessing them is entitled to the same respect, regardless of immaturity or impairment.
Thus all of Dombrowki's (1997) marginal cases qualify as bona fide holders of human rights. In other words, human moral patients are just as important as moral agents. Being a possessor of human rights does not require one to be a moral agent, but merely to have the kind of nature that is realised through moral agency (among other things).
Is this speciesism?
I contend that ultimately, the moral standing of marginal human cases derives from their membership of the human species. Is such a position "speciesist"?
The notion that mere membership of a species can confer moral standing seems absurd, as a biological boundary has no apparent moral significance. However, on the account that I have defended here, a species is much more than a boundary. It is a repository of genetic information, shared (in varying degrees) by the individuals that belong to it. This shared information defines what the telos of these individuals is. The telos is what grounds their moral standing. Species membership per se has no moral significance, but it is morally significant in an indirect sense, insofar as it determines telos.
Case study: people and chimps
Recent research (Walton, 2002; Randerson, 2002) indicates that a gene called FOXP2 is linked to language and speech ability in human beings. People share this gene with other mammals, but in human beings there have been two slight amino acid changes, believed to have occurred in the last 200,000 years. These changes are believed to have caused alterations in both human beings' face and jaw structures and their abilities to understand grammar. People with one faulty copy of this gene in their DNA cannot move their lips, tongue and mouth normally, and also have difficulties understanding language structure and grammar.
There are most likely many genes that are implicated in human beings' language ability, but let us simplify here and focus solely on FOXP2. It is easy to see why humans with a defective copy of this gene should still be said to possess human nature, as they belong to a class (Homo sapiens) whose members typically have two normal copies of this gene (one from each parent) that permits the possibility of speech and language. Even in the case of an individual with two defective copies, we could say that the information that coded for human capacities had been damaged as a result of mutations. In chimpanzees, on the other hand, the FOXP2 gene never codes for speech or language ability. These abilities are not natural to chimps, and a chimp lacking them is normal, not defective.
Finsen (1990) considers the notion of a species to be an arbitrary boundary, because closely related species (e.g. humans and chimps, lions and tigers) can often inter-breed. She asks where we should draw the line in the case of a human-chimp hybrid:
Should such a half-human primate receive the protection accorded to human subjects, or only the protections of the Federal Animal Welfare Act? What about a one-quarter human, or a three-quarter human? (quoted in Dombrowski, 1997, pp. 172-173).
It is worth remembering that humans and chimps belong to distinct species, which last shared a common ancestor five to ten million years ago. They certainly cannot interbreed to produce fertile offspring. There are no known cases of human chimp hybrids being born, so it is not known if they would even be viable.
Assuming that a human-chimp hybrid is viable, the question of what is "normal" for it simply becomes unanswerable, as it does not belong to a single biological class (species) whose members' genes define what is "normal" and "defective" for that class. A hybrid simply would not have a nature - human, chimp or otherwise. It would be an untidy amalgam of two (similar) natures, each with different sets of abilities. However, some abilities could be said to be "natural" for such a hybrid - namely, those shared by both humans and chimps. Thus communicating by hand gestures would be natural for such a hybrid, but language would not. Lacking a human nature, a human-chimp hybrid could not be accorded human moral status.
What if scientists subsequently hybridised the "50% human" DNA with normal human DNA to create a second-generation hybrid more like us - 75% human, and then 87.5% human in the third generation, and so on? There would presumably have to be a point at which the n-th generation hybrid was sufficiently close to us to interbreed with us naturally and produce fertile offspring, with human linguistic capacities. At this point, we would have to say that the hybrid had acquired human nature and human moral status.
Are super-chimps our moral equals?
Other nightmarish experiments suggest themselves (and will doubtless be attempted by some reckless researcher in the future). What if scientists tinkered with the DNA of a fertilised ovum from a chimp, and altered the FOXP2 gene, and other genes relating to human language and rationality, to make them like ours, thus conferring language ability and rationality on the chimpanzee zygote? Would the resulting super-chimp have the nature and moral status of a human being?
It needs to be borne in mind here that the number of genes that code for human rationality and language use is probably large, and that engineering all these changes at once would almost certainly result in the creation of a new biological species - assuming the super-chimp proved to be viable. For instance, human rationality almost certainly requires a human-size brain, whose cerebral cortex possesses a critical level of neural complexity, and is organised in a uniquely human way. In other words, the super-chimp would no longer be a chimp, but sui generis. As a being whose (artificially engineered) nature allowed it to reason and use language, it would have the same moral status as we do.
If, however, the super-chimp were still able to inter-breed with normal chimpanzees, it would still possess the nature and moral status of a chimp. In that case, we would have to revise our definition of "chimpanzee" and include rationality and language use as incipient traits that are part of the nature of a chimp, but whose emergence by natural means may not become apparent for thousands of generations. The moral status of chimpanzees would have to be adjusted accordingly.