1. In Chapter 3 of his book, Kitcher considers the tautology objection to evolutionary theory. Basically the objection is this: Evolutionary theory is the Principle of Natural Selection. This is the principle that the fittest survive. But what do evolutionists mean by the fittest? They mean: those that survive. So evolutionary theory reduces to the tautology that those that survive, survive. Kitcher's first point against this is that evolutionary theory is not to be identified with the single statement: the principle of Natural Selection. First, there is no such single principle -- evolutionary theory is a body of principles or, as Kitcher puts it, a collection of problem-solving strategies that use Darwinian histories. Second, the concept of fitness is not to be identified with the number of offspring that an animal produces. In fact, in modern evolutionary theory, fitness is not a property of organisms, but of genes, specifically, the fitness of the allelic pairs that make up an organism's genotype. Third, with this more sophisticated understanding of fitness, we can look to one part of modern evolutionary theory, namely mathematical population genetics, to give us precise, non-tautological probabalistic results about the survival possibilities of various allelic pairs.

2. Another type of charge levelled against evolutionary theory (again, this is a Popperian point, although Kitcher doesn't say so) is that the theory is just too adaptable -- it is so flexible that it can accommodate itself to any new observations. This is not a virtue; if the charge is admissible that would mean that Darwinian theory lacks content. As Kitcher says (p.61) `a theory that is compatible with all results explains none'.

3. But is the charge justified? Kitcher thinks not. Darwinian histories are subject to numerous checks. Some creationists deny this independent checkability. They claim, for example that geological dating of rock strata is determined by what fossils are found in those strata, and that the dating of those fossils depends on evolutionary assumptions about the dates of the organisms fossilized in the rocks. So the Creationist says that the geological record offers only a circular justification of evolutionary theory. But, as Kitcher points out, this is a complete misrepresentation. The geological system for dating rock strata predated Darwin's theory, and it was assumed that organisms found in lower strata had flourished before those found in the upper strata. But there was no commitment to the view that the upper strata organisms had evolved from the lower. And we now have plenty of independent methods of dating rock strata (e.g. radiometric testing using radioactive decay).

4. If, over the course of time, there is gradual adaptation to the environment, as evolutionary theory predicts, then it would seem that there should be a continuum of living forms -- there would be no biological categories. But there are such categories. Hence, Creationists say, evolutionary theory is false.

5. The answer to this is that evolutionary theory does not predict such a continuum. An ancestral species may split into two that then, by natural selection, go separate ways resulting, after millions of years of evolution, in two morphologically very different populations. The original splitting into two can come about, for example, when a group of organisms gets geographically isolated from the rest of the population and gets subjected to different environmental pressures.

6. Creationists are disinclined to allow the kind of laboratory evidence supplied by evolutionary theorists. But we should stress the importance of modelling in science and of experimentation on scaled-down models (e.g. wind tunnels). It is useful to study natural phenomena in the unnatural, controllable conditions of the laboratory. Indeed, this is a paradigm scientific procedure. Yet Creationists wish to reject laboratory investigations of evolutionary processes. Morris, for example, says that even if, in a lab, you succeeded in creating life from non-life, or of higher kinds from lower kinds, `this would not prove in any way that such changes did, or even could, take place in the past by random natural processes' (cited in Kitcher, p.75).

7. The difference between life and non-life, between the organic and the inorganic, has always seemed mysterious. Aristotle's conception of psuche. The mysterious élan vitale. But suppose, under laboratory conditions, one passed `lightning' through a mixture of simple inorganic chemicals and thereby produced biologically significant organic compounds such as amino acids and protein chains -- would not this be very impressive evidence that life could have come about naturally from non-life? What reason could one have for discounting as unrealistic this kind of experimentation?

8. The Creationists have a prejudice -- they believe that life just could not come about in this way, and they say that if life is produced artificially, then that is because, to the original chemical ingredients is added a special life-possessing element, namely `know-how' (the know-how of the human experimenter).

9. This suggestion is absurd. A scientist conducting any experiment (say, in superconductivity) uses his `know-how', but it is just crazy to infer that this know-how becomes part of the phenomenon under investigation.

10. Why does evolutionary theory seem to lend itself to the sort of criticisms (crazy or misguided though they may be) which we have been discussing? One reason is that, unlike in physics, the evolutionary biologist cannot make the kind of spectacular prediction that is sometimes made in physics. As Kitcher points out, evolutionary theorists just cannot make firm predictions about future life because changing environmental circumstances are quite unpredictable, potentially numerous, and probably of quite significant influence. And, of course, biological change requires hundreds of generations before change becomes significant and visible, so that none of us is going to be around to verify that the prediction was successful.

11. Yet evolutionary theory can make postdictions (retrodictions), and though perhaps not as impressive as predictions, can still be fairly impressive. Also, as Kitcher points out, paleontologists are constantly making predictions about where fossils of various types are to be found (paleontologists don't just roam the world hopefully digging in random places). Also biologists can study changes in succesive generations in microorganisns that have very short generation time, and can introduce environmental changes in the laboratory which they predict will induce mutations of a certain kind. But, as Kitcher says, the great strength of evolutionary theory lies not in its predictive power, but in its ability to explain how the present scene came about.

12. We have examined some of the various methodological complaints against evolutionary theory that Creationists have voiced. These are discussed by Kitcher in Chaps. 2-3. Chapter 4 is an examination of arguments used by Creationists which purport to show that certain well-established facts tell against evolutionary theory, and that evolutionary theory is full of counterintuitive, unsubstantiated speculation. This is, perhaps, the core of Kitcher's book, for here philosophy comes into its own in exposing and defeating poor argumentation.

13. I want to briefly review the rebuttal in Chap.4 of the various Creationist attacks, and to consider some more substantial objections that a critic of evolutionary theory might put forward. Before doing so, it is worth reminding ourselves of some of the impressive credentials of evolutionary theory that Kitcher mentioned in Chap.2. He lists a small selection of the questions that modern evolutionary theory has been able to answer: `Why do orchids have such intricate internal structures? Why are male birds of paradise so brightly colored? Why do some reptilian precursors of mammals have enormous `sails' on their backs? Why do bats typically roost upside down? Why are the haemoglobins of humans and apes so similar? Why are there no marsupial analogues of seals and whales? Why is the mammalian fauna of Madagascar so distinctive? Why did the large carniverous ground birds of South America become extinct? Why is the sex ratio in most species one to one (although it is markedly different in some species of insects)?' If we look at the details of the answers to these questions, we see that evolutionary theory provides a unified account of all these phenomena; the theory meshes in with geological accounts of changes in the environment and with other independently verifiable scientific theories, and it gives rise to important new areas of scientific investigation.

14. One argument of the Creationists, which perhaps echoes the feelings of outsiders too, is that when we examine such complex structures as the eye, or even when we look at the DNA molecule, it simply seems incredible, even allowing for the evolutionary time scale, that such systems could have come about from the random mutations that are the driving force behind evolutionary theory. In addressing this point we should distinguish between what is irreducibly random (e.g. radioactive decay, according to quantum theory) and what is apparently random because determinable in principle, but not in practice. But processes of both kinds are subject to physical and chemical law -- although the former only to probabilistic laws: we should not equate irreducible randomness with pure chaos. The point here is that if a system is purely chaotic then any future state is not even probabistically calculable from its present state. Thus, as Kitcher points out (pp.88-89) `Quantum chemistry explains in great detail why the elements regularly combine in just the ways that they do. Thus there is no reason to wonder whether the order found in biochemical reactions proceeds from some mysterious source'. The development of beautiful complex structures from random mutations is illustrated by the morph program from Richard Dawkins' The Blind Watchmaker.

15. Another argument that Creationists use against evolutionary theory is what we might call the argument from thermodynamics. In particular, it is the second law of thermodynamics with which, according to the Creationists, evolutionary theory conflicts. Following Kitcher (p.90), I state the second law as follows: `The entropy of a closed system increases with time ... i.e. if we have a thermodynamically closed system, the total amount of energy within it remains constant through time, but an increasing proportion of that energy becomes unavailable to do work. (Alternatively, the system becomes even more disordered.)'

16. The reason that Creationists think that the second law is in conflict with evolution is that, as they interpret it, the second law demands a trend towards disorder, randomness, whereas Darwinian theory predicts the opposite trend towards increasing complexity and organization. In reply, we could say first, as mentioned above, that evolutionary theory doesn't predict complexity. Further, Creationists overlook the crucial clause in the second law about the systems in question being closed. But it should be obvious that the systems relevant in Darwinian histories are open, and where entropy decreases over time. The reason is obvious: in all the systems of organisms and genealogies and lineages there is a constant inflow of energy from the sun: we are not dealing with closed systems. Suppose however, that in answer to this we say that if we include the sun and the rest of the universe, then we are dealing with a closed system. We can agree, and can grant that the entropy of this system as a whole increases. But that tells us nothing about entropy variation at the local level, where there may be pockets of decreasing entropy.

17. Another charge often made by the Creationists is that mutations, which are at the heart of evolutionary theory are rare and almost invariably have an adverse effect. However, Kitcher (p.97) quotes figures to show that for homo sapiens, the number of mutations arising in one generation is 8 billion. In other words, although it may be true that the mutation rate per locus is low (roughly one mutation per 100,000 loci), the rate per zygote is one mutation per zygote and the rate per population is of the order of one billion per population. As to the claim that all mutations are harmful, the truth is that some mutations are harmful in some environments, but some, in the context of its immediate surroundings and of the more remote environment are advantageous. A well-known example is the development in many species of insects of resistance to pesticides such as DDT. The mechanism for this is well known: `a change at a single locus can produce (or increase the rate of production of) enzymes that allow the pesticide to be detoxified' (p.100).

18. The objection to evolutionary theory that I find most powerful is simply that there would not have been sufficient time for the development of the extremely complex biological systems with which we are all familiar. We know, for example, from the drawings of the ancient Egyptians, that domestic animals haven't much changed over the last 4000 years. How could the development of, say, the human eye have taken place in the time during which the earth has been in existence ? One answer to this is that the Earth has been in existence for much longer than evolutionists usually allow.

19. The Creationist may well counter that, for example, the number of mutational steps needed for the evolution of the horse must be well over a million. And if we look at the probability of these million changes occurring, given that there is a 50-50 chance of each change occurring the probability is 2^1000000 (same as the chance of a coin landing heads one million times in a row). Hence (say the Creationists) the probability of a horse evolving is negligible. But Kitcher points out (p.104) that this argument confuses apparent improbability with irreducible improbability: given the initial conditions then (assuming no uncertainties due to quantum effects) we could say that the evolution of the horse is a deterministic certainty -- just as, given the initial conditions of a deck of cards, we can say that the probability of getting dealt a given hand of 13 cards is certainty. With no statement of the initial conditions, the probability of getting dealt that hand is about 1 in 4*10³¹. Besides, it's wrong to assume, as the Creationists' calculation does assume, that these mutations occur one at a time. Mutations are occurring all the time in populations.

20. Creationists dwell on the fact that there are gaps in the fossil record. They think that, if evolutionary theory were true, there would be fossils corresponding to all the organisms described in Darwinian histories. The first point to be made againt this is that only a tiny fraction of organisms get fossilized, so we should not expect a complete fossil record. Second, one would expect that different organisms would have different prospects for fossilization because of the nature of their environments. Molluscs, for example, would stand a good chance, but birds and insects are `likely to die in places where sedimentation is not occurring and where their delicate skeletons will be extremely vulnerable' (p.107).

21. There are several cases of large-scale evolution accounted for by modern palaeontology. Of course, Creationists will question such accounts. Duane Gish, for example, holds that transitional forms have many structural dissimilarities. That is true, but Gish is making too heavy a demand for evidence -- palaeontologists count themselves lucky if they can find transitional forms that are similar in just a few crucial respects.

22. Creationists argue that even if evolution occurred, the half-way stage, say, when a creature was burdened with an incipient wing, would confer disadvantage, so that trait would be selected against and wings would never develop. This is a poweful objection, but even though responses to it (e.g. Kitcher, p.117 ff., R. Dawkins, The Blind Watchmaker, Chap.4.) may not be compelling, the point to be made here, surely, is that this is one of the problems on the agenda for evolutionary theory, not a devastating criticism that should make us abandon the theory and join the Creationist camp.

23. Kitcher is rather disdainful of certain other findings that Creationists say are fatally damaging to evolutionary theory. For example, the Paluxy river bed where, so the story goes, human footprints traverse dinosaur footprints; Rhodesia, where there are cave drawings said to depict dinosaurs; Glacier National Park, where the evolutionists' ordering of rock strata is `inexplicably' reversed. According to Kitcher, none of this `evidence' is to be taken seriously. The cave drawings are not drawings of dinosaurs, but are bad representations of other creatures. (Another possibility, not mentioned by Kitcher, is that they are drawings of fantasy creatures.) As for the rock strata, it is not infrequent for strata to become deformed during tectonic movement, with older rocks being thrust over younger. The Paluxy river bed is in central Texas, and, during the depression, local inhabitants made money by carving `dinosaur' tracks in the rocks. So even Creationists (at least the honest ones) no longer cite this `evidence'.

24. A recent attack on evolutionary theory by a philosopher is David Stove, `So You Think You Are a Darwinian?', Philosophy 69 (1994), pp.267-277. Stove lists what he takes to be 10 `obviously false' Darwinian beliefs. Some of these are from modern evolutionary sociobiology. For example:

® It is to a mother's advantage that her child should be adopted by another woman.

® All communication is `manipulation of signal-receiver by signal-sender.'

® Homosexuality in social animals is a form of sibling-altruism: that is, your homosexuality is a way of helping your brothers and sisters raise more children.

® In all social animals, the altruism (or apparent altruism) of siblings towards one another is about as strong and common as the altruism (or apparent altruism) of parents towards their offspring.

® `... no one is prepared to sacrifice his life for any single person, but ... everyone will sacrifice it for more than two brothers, or four half-brothers, or eight first-cousins.

® Every organism has as many descendants as it can.

® In every species, child-mortality -- that is, the proportion of live births which die before reproductive age -- is extremely high.

® The more privileged people are the more prolific.

® If variations which are useful to their possessors in the struggle for life do occur, can we doubt (remembering that many more individuals are born than can possibly survive), that any individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind ? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed.

® All animal life, including that of man, is purposeless: life has no higher purpose than to perpetuate the survival of genes.

25. I cite Stove's first proposition last. It is one that is enthusiastically defended in two recent books, Richard Dawkins' River out of Eden and Daniel Dennett's, Darwin's Dangerous Idea. (Dawkins has adapted one of the chapters of his book for an excellent article in Scientific American, November, 1995, pp.80-85). Is the idea that life has no purpose true or, as Stove would say, `obviously false' ?

26. One of the reasons why people are resistant to the idea is that human beings clearly have purposes, so how can our existence be purposeless, how can we be inhabitants of what Dawkins calls a `universe of indifference' ? And if evolutionary theory is correct, and we are the final products of a long process that took place over millions of years, how can that process have no point ? `If we are the products of natural selection, then we have been selected (chosen)', someone might say.

27. As Colin McGinn points out, in a review of Dennett (Times Literary Supplement, November 24, 1995) the term `selection' is misleading here. It's not just organisms, but everything in nature that is `selected' in the sense that some things better survive the destructive forces of nature -- a mountain made of granite (McGinn's example) is less likely to be eroded by wind and water than another mountain with a sandier constitution. We are quite happy to say that there is no purposive agency behind the existence of granite mountains. Genes mutate; this is just a `blind', mechanical process, and some mutations render an organism less likely to destruction.

28. If evolution doesn't aim for anything, then it doesn't aim for complexity. McGinn raises the interesting question of why complex forms emerge -- given that simple structures (like mountains) seem to be more robust. Here there seems to be a fact not explained by evolutionary theory. The theory does not predict development over time from the simpler to the more complex, but it is a fact that some presently existing organisms (such as ourselves) are extremely complex. `The best survivor of all would be some hard little simple object that could not be broken down by the forces of nature; so why should relentless pressure towards ever greater durability [i.e. natural selection] produce such soft, friable, complex creatures as we see all around us ?' Two further problems raised by McGinn: There would be a selectional advantage in a mutation which made genes responsive to changes of phenotype, so why is it that Lamarckian organisms never evolved ? And how (and why) did consciousness and sentience evolve ? These are problems for the theory of evolution, not refutations of it.

29. Distinctive organisms are deposited in successive strata of rock. At the lowest level are the fossilized remains of marine invertebrates. In higher strata we get fish and, higher still reptiles, then birds, then mammals. The obvious assumption to make here is that the organisms at the lowest level were the first occupants of Earth and that the animals fossilized in higher strata are those that existed on Earth when these strata were added. This view, though it carries no commitment to the idea that the later organisms evolved for the earlier ones, nevertheless comes into conflict with Creationism, because that theory holds that all organisms were created at once.

30. One of the `theories' of Scientific Creationism is Flood Geology, which is an attempt to explain the fossil record. According to the theory there was on Earth a cataclysmic flood which destroyed virtually all animals and deposited almost all the fossil-bearing rock. Water came from inside the Earth and from a vapour canopy (see Kitcher, p.128); Noah saved a pair of each of the land-dwelling animals in his ark; most of the rest perished. They were drowned, engulfed in mud and eventually became fossilized. The flood ended partly through evaporation of the water, and partly because mountains erupted forming huge basins, so the flood waters became lakes.

31. The story is certainly charming, but is it plausible? Well, we know that there is water trapped beneath the surface of the earth, and it is not inconceivable that some event, e.g. a large meteorite striking the Earth at great speed, could have triggered its release and perhaps also set in motion a chain of events leading ultimately to the eruption of mountains. But this really is a `Just So' story. And does it square with other scientific facts? Suppose, for example, that physics tells us that there just could not have been sufficient quantity of water beneath the Earth's crust to have produced global flooding. Then the Scientific Creationist would have to invent not just an alternative biological theory, but also a creationist physics.

32. One problem with the theory of Flood Geology is that it offers no detailed account of any aspect of the pattern of fossilized deposits. Morris supplies some details but these are specious and leave many unanswered questions (see Kitcher, p.131, in Chapter 5 of his book, which is the reading for this week and is in the Department’s xerox collection).

33. Kitcher is wrong though, it seems to me, to dismiss the theory outright, since it does lend itself to appropriate methods of scientific testing. For example, we have now witnessed and studied scientifically many floods and volcanic eruptions: We can make rough predictions of earthquakes and meteorologists can tell when conditions are ripe for the occurrence of massive storms. So it is a genuine scientific question whether, under particularly unfavourable conditions, a global storm could erupt, resulting in a flood lasting 371 days. And the meteorite suggestion is not outlandish: it is part of regular science that one of the historically major climactic changes on Earth was the result of a mile-wide meteorite hitting with great force, creating dust clouds which blotted out the sun's rays for a lengthy period.

34. Further, it is possible to produce computer programs to model a great flood, and this could confirm or falsify the possibility of the sequence of turbulent events which, according to the Creationists led to the fossil deposits. This type of independent check is not available for the alternative fantasy explanation (`theory-sketch') that Kitcher contrives (p.132) and it is disingenuous for him to claim that `from a scientific point of view, my proposal is no worse than Morris' Flood Geology'.

35. Although philosophers such as Stove and McGinn raise problems for evolutionary theory, they are not supporters of Creationist `Science'. But does Creationism have decent scientific credentials? If it is a science, it is a particularly stagnant one. Where are the next major breakthroughs? What are the hot areas of research? In what fields is the liveliest controversy now taking place? These are the sorts of questions that one can ask of genuine science, but Creationist Science does not seem to admit of this kind of question.

36. The basic tenet of Creationist Science is that all organisms were created during the first six days of the Earth's existence. This can be accepted as an article of faith, and Kitcher has no objection to that. What he opposes is Creationism posing as bona fide scientific theory.

37. If Creationism is scientific theory, then it is very thin. One could hardly see how there could be enough material for a one-semester course in the subject, and certainly not enough for the six years, @ 4 hours/week typically allocated to Science in secondary schools.