A collage of organisms. Courtesy of Azcolvin429 and Wikipedia.

Table of Contents	Part One	Part Two	Part Three	Part Four	Part Five	Part Six	Part Seven
Part Eight	Part Nine	Part Ten	Part Eleven	Part Twelve	Part Thirteen	Part Fourteen	Conclusion

Zack, on your Website, you've expressed a desire to keep religion out of the science classroom. I agree. You also want to make sure that high school students are not exposed to junk science.

So here's what I believe American high school students should be taught about origins, in a nutshell. Imagine that a science class at a public high school is just about to begin a course unit on the origin and evolution of living things, and that the science teacher is giving an overview of the unit. This is roughly how I'd teach it, if I were addressing a class. I've done my best to keep it as scrupulously fair and even-handed as possible, in the light of the current evidence. Here goes.

Hi everyone. We're about to begin a new unit on the origin and evolution of living things, and I thought I'd begin with a brief overview, so as to clear the air and highlight the main points.

First, I'd like to say a few words on science. As you should all be aware by now, science isn't in the business of proving hypotheses, although it can disprove them. Science deals with evidence; proof is for mathematicians. Not all scientific hypotheses are equal. Some hypotheses are rather vague; scientists don't like them very much. Scientists like detail, because it makes a hypothesis easier to test. Other hypotheses are detailed, but narrow in their explanatory scope. That frustrates scientists, because they like to explain as much as they can. However, a few hypotheses are both detailed and very broad in their explanatory scope: they're called theories. When a scientific theory is corroborated by many different lines of evidence, and survives repeated attempts to disprove or invalidate it, then it's accepted in the scientific community as a fact. That doesn't mean it's proved, of course; it could still be wrong. What it means is that scientists are willing to publicly affirm that it's very unlikely to ever be proved wrong – at the risk of considerable embarrassment to themselves if it is.

Currently, there are multiple converging lines of scientific evidence supporting claims that the universe we live in is approximately 13.7 billion years old, that the Earth is about 4.54 billion years old, that life on Earth appeared three or four billion years ago, and that all living things are descended from a common ancestor. These are currently accepted as facts by scientists. I'm not telling you that you have to accept them; I'm just telling you that scientists working in the field do accept them, and that these assertions have survived numerous attempts to falsify them, so scientists are not inclined to argue about them.

You've just finished a unit on the origin and development of the Universe, followed by another unit on Earth history, so I won't waste time recapping the scientific evidence for the age of the Earth or the Universe. I take it you're all familiar with that. There are people who think that the Universe is relatively recent - only a few thousand years old. I can't disprove that, and I'm not going to make some absolute pronouncement that it's wrong, period. What I will say is that scientists currently have a picture, supported by many converging lines of evidence, of a much older Universe, and it would take a lot to dislodge that view - and I do mean a LOT. While there are a few strange phenomena in the cosmos that continue to puzzle scientists - like the nature of dark energy (if it's real) and the rapidity with which galaxies formed - there's no class of phenomena known to science which systematically points to a much younger age for the Universe. Please bear in mind also that scientists have never been in a position where they could explain everything: there's always something new on the horizon. That's the nature of the quest.

All right. Now let's talk about living things. As you'll find out in this course, living things share a suite of common properties, which we'll be examining later, that cannot be readily explained unless we assume that they're all related, and the family trees of different kinds of organisms that have been derived by independent techniques tend to resemble one another very closely – so closely that the odds of this being due to chance are astronomically low. Biologically speaking, living things certainly look as if they share a common ancestry, and biologists take this fact for granted in their research. It explains an awful lot, and there's nothing that disconfirms it. There might be arguments about exactly how two organisms are related, but not about the fact that they are related. To give you an example: most biologists think that our nearest relative is the chimpanzee; a few would say both the chimpanzee and gorilla, and there’s even a minority view that the orang-utan is our closest relative. But there's no scientist who'd say our nearest relative is the Giant panda, or even the baboon.

If you're looking for evidence of evolution in the field, I can tell you it has been observed at the species level, but not at higher levels. Most scientists would say that's because we haven't been around long enough to chronicle major changes occurring in nature, which are believed to take millions of years. On the other hand, bacteria reproduce pretty quickly, and we've bred zillions of them in the laboratory during the past century or so, under all kinds of conditions, but the amount of change we've observed is relatively slight. Nothing terribly new has appeared - no major innovations or structural changes. That's very odd. Most scientists would say, though, that that's a bit unfair: to make a really fair comparison with evolution, what you'd need is an experiment in which not only bacteria, but also their hosts (like us) were evolving through millions of generations - and of course, that'd take too much time.

If you're looking for fossil evidence for evolution, you should be aware that most organisms, being soft-bodied and small, haven't left many traces of their evolutionary history in the fossil record, so the fossil record is necessarily patchy. As you know - or should know - human beings (Homo sapiens) belong to the same family (hominids) as chimps, gorillas, and orang-utans. That family belongs to a larger group called an order (primates) which in turn belongs to an even bigger group called a class (mammals), which belongs to a phylum (chordates). That's the group which includes all back-boned animals, as well as a few other anatomically similar creatures. So I guess you're asking: what's the fossil evidence for evolution at these different levels? Well, there's quite a lot of fossil evidence for evolutionary transitions at the level of the family (e.g. elephants) and there is good fossil evidence for some (but not many) transitions at the level of the order (e.g. land animals to whales) and even a few transitions at the level of the class (e.g. reptiles to mammals and reptiles to birds), but there are no transitional forms known yet at the level of the phylum (e.g. simple animals evolving into mollusks, arthropods and chordates), let alone at the level of the kingdom (e.g. simple creatures evolving into the first animals). In the next few years, however, we might well be able to identify fossil precursors for some of the major animal groups found on Earth today, as we get a better picture of how animals emerged. However, I should tell you that most or all of the 30 or so main groups of animals living today are now known to have appeared at about the same point in time: they emerged over a period of approximately 20 million years. Now, 20 million years might sound like a long time, but it's just an eye-blink, compared with the 4,540-million-year history of the Earth. So the question of why nearly all these groups of animals appeared around the same time is currently a major unsolved mystery of science.

I would also like you to bear in mind that while most scientists believe that the sorts of minor changes in organisms that they've observed in the lab and in the wild would, over the course of millions of years, add up to major evolutionary changes, such as the appearance of new organs or body plans, that's an extrapolation. It's the current working hypothesis, which is accepted by most biologists, but scientists don’t have any positive evidence that minor changes add up to major changes over time. Their main evidence for this hypothesis is negative: they claim that there are certain odd features of bodily organs and complex biological systems which would be very difficult to explain if they were made suddenly from scratch, so they reason that these organs and systems must have developed step-by-step.

As I said, animals belong to about 30 different major groups or phyla, which are distinguished by their body plans and their patterns of gene regulation when they develop. These patterns of gene regulation are absolutely eye-popping: they look for all the world like logic circuits. What's more, the components of genetic regulatory networks are highly inter-dependent, which makes it extremely difficult for scientists to envisage how they got started. Anyway, most or all of the 30 major groups of animals appeared approximately 520 million years ago, over a time period of just 20 million years. How the body plans for these 30 groups of animals originated is currently a scientific mystery, and we're nowhere near solving it. It's not helped by the fact that about 50 new cell types for these animals' body parts would have had to originate over a relatively short geological period: 100 million years, if we're very, very generous. This would represent a major acceleration in the pace of evolutionary change, compared with what happened in the preceding three billion years. Right now, though, the origin of any new cell type is something that scientists don't have a handle on, let alone the relatively sudden origin of 50.

How life emerged is a mystery, too. There is no good scientific hypothesis for the origin of life at the present time. A living cell is dazzlingly complex – much more so than any machine or computer designed by scientists or engineers. A living cell is also much more efficient in the way it works than any machine we've ever designed. If you want a mental picture, try and imagine a computer chip with a wall around it, only a few micrometers in length, that can eat, excrete, grow and replicate with a high degree of accuracy. Even a humble bacterium is like a miniature city, and it hums along continually, with different parts doing thousands of different tasks. None of these parts gets in the way of the other parts; they all go about their little jobs. And that's what the simplest cells do.

So that brings us to the question: how did the first cell appear? There are two possibilities. Most scientists believe that step-by-step chemical processes, occurring in series and/or in parallel over hundreds of millions of years, gave rise to the first living organism. The other possibility, which a few scientists subscribe to, is that some intelligent agent designed the first living thing.

There are problems with the first view. The genome of living things contains a digital code. Intelligent agents can make codes, of course, but can natural processes that lack foresight generate codes? Apart from intelligence, we currently know of no process that can generate a code, even over a long period of time. But there’s more. Each living cell also contains many complex parts, each of which performs a specific task within the cell. The ATP synthase molecule is one example. At the present time, we simply don't have a scientific discipline that is capable of explaining the origin of complex systems that can perform a task, on a comprehensive basis. We really need a new kind of science here, and we don't have it yet. For the kind of complexity we find in living things is special. It's different from the complexity of a string of random numbers, and it's different from the regular, repetitive order of a crystal, too. A final problem with a step-by-step scenario for the origin of life is that the proteins that we find inside cells fold up in a very specific way, and you can’t just make them by stringing amino acids together willy-nilly. You've got to assemble the right ones, in the right order. The vast majority of long-chain molecules that you can make from assembling amino acids at random are biologically useless: they can’t do anything, because they don't fold the right way. The problem here is that the odds of Nature finding the right long-chain molecule at random are astronomically low – much lower than the odds of finding a needle in a haystack – and unfortunately, there don't appear to be any laws of Nature that would make the task of hitting on a long-chain molecule that can actually do a task – i.e. a protein – any simpler. To compound the problem, each living cell contains literally thousands of different types of proteins. So how did they originate? Figure that one out, and you'll get a Nobel Prize, I can promise you.

That leaves the second view: that life itself was designed. Certainly this would explain the complexity of life in one stroke, if we assume the designer to be very intelligent. However, I should tell you that most scientists dislike this view because it sounds too vague: at the present time, we have no way of discerning the identity or modus operandi of the designer, using scientific methodology. Who is this mystery designer and how does he, she or it work? What are the designer's goals? When and where did it produce the stunning complexity we find in living things? Did it front-load the information to make living things into the universe at the Big Bang? Or did it act later on, making the first cell and pre-packaging it with information that would allow it to evolve into the different kinds of living things we observe today? Or did it act on numerous occasions in history – the dawn of life, the appearance of animals’ body plans, and perhaps also helping out at major evolutionary hurdles? And how major are we talking about, anyway? Did the designer accelerate the evolution of whales from land animals? And why did it still take ten million years? Why not a single generation, or just a few generations? And what about organs and systems which seem to have been badly designed, like the male reproductive system? So there are problems with both views of the origin of biological complexity: one currently has no answers, and the other has an answer, but for many scientists it seems a vague answer, and it's not without difficulties. You'll have to make up your own minds on these issues. Of course, there is a natural human temptation to just side with the majority opinion, and think no further about an issue. But majorities aren't always right, and every theory that scientists now accept as fact was, at one time or another, a minority view. So my advice would be: keep probing. These are important issues.

Finally, if you're wondering about the origin of animal and human minds: scientists have a fairly good idea how animals acquired their cognitive capacities, but the fact that animals have conscious experiences remains a very curious conundrum. It's odd, from a scientific standpoint. Of course, there are lots of hypotheses, but we still don't know why animals are consciously aware of anything at all. As for human beings: well, of course there are fossils that appear to link humans with their chimpanzee cousins fairly well (at least on the human side - we don't have many fossils of chimps), but the origins of human reasoning, language, art, morality and religion remain an almost complete mystery – which unfortunately doesn't stop so-called experts from writing best-selling books claiming they've solved the mystery! All we can say for sure is that our distinctly human cognitive traits emerged somewhere between 90,000 years ago and two million years ago. Whether they emerged simultaneously or at different times is still a subject for controversy. Mentally speaking, though, humans do appear to be in a category of their own compared with other animals, notwithstanding the wealth of scientific evidence that humans share a common ancestry with chimps and other apes. Make of that what you will.

I know some of you might be inclined to dispute the statement that human consciousness is unique. I'm not trying to put down other animals down. But facts are facts. I'll just mention a few ares where humans appear to have special abilities. Let's start with memory. Autobiographical memory is a fairly well-defined term in the field of psychology. It was originally coined by a guy named Tulving. Basically, it means the ability to mentally review the whole course of your life, from your earliest memories as a child, right up to the present time. Because humans have autobiographical memory, they can travel back in time, mentally, and recall events from their past at will. However, there's no evidence that other animals can do that. There are a few birds, called scrub jays, that can recall where they've squirreled away nuts a few months previously. But that's totally different from being able to view the whole course of your life in a single sweep - let alone being able to answer questions like, "Where were you on September 11th, 2001?"

Metacognition is another area where there's a huge qualitative difference between humans and other species. Metacognition means being aware of your own mental states - what am I feeling now? - being able to describe them, and also being able to transform them - for instance, changing the way you respond to setbacks, or to people who get on your nerves, or things that scare you. At the moment, we have experimental evidence suggesting that other primates seem to know when they're sure about something (like where some food is located) and when they're not sure. And that's it. There's no scientific evidence that a chimp can answer the question, "What are you thinking now?" There's no scientific evidence that a chimp can mentally resolve to stop being so mean to another chimp that it regularly picks on, and decide to be nice to that chimp instead. To some extent, we are capable of changing our mental states - for example, depression - simply by changing our attitudes. But there's not a smidgin of evidence that chimps can do that.

This leads me to the next area I want to discuss: rationality. Certainly, there are animals which are capable of some quite impressive feats. You've probably heard of Betty the crow, which can make tools with its beak, in order to get a piece of food that's out of reach. But we can't ask Betty: "Why did you do it this way, and not that way?" That's a very important point. It reminds me of something a mathematics teacher once said to me. She said: "It's not enough just to get the right answer. You have to be able to explain why it's right. If you can't do that, then you don't really understand." Until crows can justify their actions to us, we should remain skeptical of claims that they are capable of genuine reasoning. "All right," I hear you say, "but they can't talk to us. Maybe they can talk to each other though. Maybe Betty can teach her offspring the reason why, in bird language." OK. Let's go with that. Let's imagine Betty teaching her offspring how to make a tool for retrieving meat, with its beak. "Don't bend the stick that way. Bend it this way." - Why, mummy? "Because if you bend it this way, it can pick up a piece of meat, but if you bend it that way, it can't." This short dialogue contains only simple little words, but the problem should be immediately apparent. The meaning of words like "if," "why," "but," "can" and "can't," cannot be conveyed to someone who does not understand them, through bodily gestures alone. How would a baby bird ever pick up these words? You might say that crows have a language faculty that lets them do that. Fine: let's see your evidence. Until we have scientific grounds for saying that crows possess a language at this level of abstraction, we should react skeptically to claims that they can reason.

Humans also have a uniquely rich concept of self. You've probably heard of animals like chimps, dolphins and maybe elephants, that can recognize themselves in a mirror. But the mirror test is ambiguous: it doesn't answer the philosophical question of whether they are recognizing themselves as subjects or simply using the mirror as a tool to explore their own bodies. There's no evidence to date that a chimp or dolphin has a concept of itself as a person or agent. Closely related to this is the issue of whether animals have a theory of mind. Do they know that other animals have minds of their own? Do they realize that each animal in their group can feel pain, like itself? Do they understand that each animal has its own perspective - that what animal A can see, animal B might not be able to see? Do they understand that some animals know things that other animals don't? To date, scientists haven't found any convincing evidence that they do. That doesn't mean they never will; what it means is that the onus is on those making these extravagant claims about animals' cognitive powers to justify them.

Language is another area where there's a huge difference between humans and other animals. Human language is based on a set of rules relating symbols to their meanings, allowing speakers to form a potentially infinite variety of possible new sentences from a finite number of words. Now, there are animals who use certain vocal utterances to refer to certain things, and some (e.g. dolphins) even appear to use them as names. But there's no evidence that they actually think of these vocalizations as symbols with a meaning which is defined by some rule, and there's absolutely no evidence that these animals ever think about "bending the rules" a little, when they get creative - as poets sometimes do when writing poetry.

Finally, I'd like to meantion certain things that are found in every human society studied to date, but not in any other species of animal. I'm talking about things like art, story-telling, religion, and an ethical code. Now, some of these features of human societies are very hard to define in rigorous scientific terms, and you will find people who say that we should ignore them for that very reason. But we don't know exactly what life is, either - yet that doesn't stop scientists from looking for life on other planets, and even on comets.

So the upshot is: we're very peculiar animals indeed. Future research might alter the picture, but we do seem to be different from other animals.

Before I finish, let me just say that this is a science class, so I can't comment on any religious or metaphysical claims. What I will say is that science certainly doesn't rule out belief in an Intelligent Being who created Nature, or designed it, or both. Even if there is such a Being, the fact that it created or designed Nature doesn't tell us whether this Being has a body or not - all we can say is: if it does, it's not subject to the laws of our cosmos. Nor can we tell whether this Being would possess finite or infinite intelligence.

A lot of people argue that the existence of sub-optimal designs in Nature precludes their being the result of intelligent planning. However, it's difficult to say what an optimal design would be, when you have to satisfy multiple competing constraints. What looks sub-optimal might be the best of a bad set of choices. Also, logically speaking, things that are intelligently designed don't have to be optimally designed. Most of the things we design aren't optimal - indeed, some machines are even designed not to be optimal, so people will come back and buy a replacement when they break down. Just ask any auto maker.

I'd also like to remind you that the question of whether life had a Designer is logically independent of the question of whether this Designer is benevolent, so the argument that life couldn't have had a Designer because lots of people and animals die painful deaths is fallacious: it assumes that the Designer's over-riding goal was the minimization of death and suffering. Maybe; maybe not. Even if you decide to postulate a Designer in order to explain life, there are many goals that this Designer might have. The reduction of pain and suffering is just one among many possible goals.

Finally, a word about consciousness. There are people who don't believe that life was designed, but who nevertheless believe that the emergence of human and animal consciousness must have been planned. That's another possible view. Of course, there are some people who believe that these things were all designed, just as there are some people who believe that none of them were. You'll have to make up your own minds on those matters.

Well, that's it, in a nutshell. I'm a science teacher; I won't be examining you on your particular beliefs, but on what you know about the current scientific worldview. So when I ask you how old scientists think the Earth is, I expect you to be able to answer: 4.54 billion years, and I expect you to be familiar with the reasons why scientists think that. And when I ask you why scientists believe living things spring from a common stock, I'll expect you to be able to list at least half a dozen major reasons why. But I won't be asking you what you personally believe. This isn't the Inquisition. And when I ask you what the major outstanding scientific problems for any naturalistic theory of abiogenesis, I certainly won't be asking you how you think life got started, and I won't be asking you whether you think these problems are soluble or not. That would be too speculative for a high school science class. I realize that many of you have strong opinions on this subject, and if you want time for a classroom debate later on, that's fine, but we have to get through the curriculum first, so without further ado, let's get to work.

All right, Zack. The science lecture is over. I didn't use the word "God" once, and I tried to be scrupulously fair to both sides. You tell me: why would you find the foregoing account objectionable, in a high school science classroom? Or perhaps you wouldn’t?

Table of Contents	Part One	Part Two	Part Three	Part Four	Part Five	Part Six	Part Seven
Part Eight	Part Nine	Part Ten	Part Eleven	Part Twelve	Part Thirteen	Part Fourteen	Conclusion