1. Already, in this course, you have looked at the question of how to demarcate science from non-science, and have investigated whether induction is the method of science. In the next two lectures, we shall take as a test case the claim of Creationism to be a science – to be offering a genuine scientific alternative to the theory of evolution. One text that is devoted to this issue is Philip Kitcher, Abusing Science: The Case Against Creationism (Cambridge MA, MIT Press, 1982). You can tell from the title which side Kitcher is on! You may want to supplement Kitcher with another source, such as Chapter 2 of Kim Sterelny and Paul Griffiths, Sex and Death (University of Chicago Press, 1999).

2. Kitcher deals with a movement known as Creationist Science which threatens to push science backwards. The science under attack is evolutionary biology, but if the attack is successful, many other parts of science are under threat. For many other sciences contribute to confirming -- are `intertwined' with (p.4) -- the claims of the theory of evolution and, if it falls, they too lose credibility. Second, many aspects of the Creationists' attack could, if successful, be turned on other areas of science.

3. Creationism is the view that the Book of Genesis is literally true, and Creationist Science is an elaboration of the claim that Creationism can be scientifically established. It consists therefore of a positive agenda -- to give a scientific account of the Genesis story -- and a negative agenda -- to discredit scientific work (principally the Theory of Evolution) which leads to conclusions inconsistent with Genesis.

4. Contrast between the two theories: Evolutionary theory says that species develop in a natural way with no purpose (this is what Daniel Dennett calls `Darwin's Dangerous Idea'); Creationism says that God fashioned the diversity of creatures in a magnificent burst of activity lasting six days. Evolutionary theory says that the developmental process took millions of years; Creationist Science holds that the world was created only a few thousand years ago.

5. Some states in the U.S.A passed laws forbidding the teaching in schools of evolutionary theory, and some of these laws were not repealed until the 1960s. Some states have passed `balanced treatment' laws requiring that equal school time be given to evolutionary theory and to the Creationist alternative.

6. A few years ago, some legislation was enacted in San Francisco requiring balanced treatment in the teaching of English Literature -- many of the standard texts are to be dropped from the list of required reading, to be replaced by works written by black authors, by women and by gays. Is it more (or less) acceptable to insist on `balanced treatment' in literature than in science?

7. Kitcher intends his book to be `a manual for intellectual self-defence' (p.4) against the Creationist onslaught.

8. What is the Theory of Evolution? Kitcher tells us (p.7) that its main thesis is that species are not fixed and immutable, that many different species spring from a common source. There has been considerable debate in the Philosophy of Biology about what constitutes a species. A widely accepted view is that two species are different if members of one cannot interbreed with members of the other. A classical discussion is M. Ghiselin, `A Radical Solution to the Species Problem', Systematic Zoology 23 (1974), pp.535-544.

9. Before Darwin, Lamarck had developed a very different kind of evolutionary theory. According to him, individual creatures change in the course of their lifetime so as to better accommodate themselves to their environments (for example, giraffes stretch their necks so as to reach foliage high in the trees). These improved characteristics are passed on (according to Lamarck) to the next generation, who likewise improve their characteristics.

10. In Darwin's theory, the mechanism for change is entirely different; it is natural selection. This term is not a particularly happy one, since selection is normally thought of as deliberate, as purposive, but Darwin's is not a teleological theory. According to Darwin, the creatures in a particular generation differ from each other in small ways. Some have characteristics which benefit their chances of survival and hence of reproduction. Those characteristics are inherited by the offspring so the incidence of that characteristic in creatures of that kind increases over time.

11. What Darwin was not clear about was how variations between members of a species arose, nor about how the fitter creatures passed on their characteristics to the next generation.

12. Unless variations occur within a group, then no member of that group will be at an advantage and there would be no impetus for evolutionary change. However, with variations, some members of the group secure a reproductive advantage. If they reproduce, and the favourable trait is inherited, then, after generations, that trait becomes widespread among the population. Inheritance is thus the engine of change. But Darwin did not have a clear idea about how variation and inheritance worked.

13. Part of the answer had been available since 1866 in the writings of Mendel, that Darwin and others overlooked. Darwin had held that the gross anatomical features of parents are `blended' in their offspring. There is obviously something unsatisfactory about this view. For, whereas it makes sense to talk of `blending' the parents' height (say) what could be a blending of their different eye colours? Mendel's idea was that an organism had an underlying structure which explained patterns of change and determined the characteristics of succeeding generations. There are what he called `factors' (what we now call `genes') which are inherited unchanged (no blending), the characteristics of an offspring being shaped by the genes it receives from each parent. Each fundamental characteristic of an offspring is governed by two genes, one contributed by each of the parents, and, of course, when that offspring itself mates, it transmits, for each fundamental characteristic, just one gene from each pair (either the one inherited from the mother or the one inherited from the father) to its own offspring. It may, for example, transmit its mother's gene for eye colour, its father's gene for straightness or curliness of hair (if that is, indeed, a fundamental characteristic).

14. Alleles are alternative forms of a gene. So, for example, the gene for blue eye colour is an allele of the gene for eye colour. Similarly, the gene for brown eye colour is an allele of the gene for eye colour. If, for a given fundamental characteristic, an individual has a pair of the same alleles, he is said to be homozygous for that characteristic; heterozygous otherwise. If an individual is heterozygous for a given characteristic, then that characteristic assumes the form of the dominant allele.

15. Distinction between genotype (the totality of an organism's genes) and the phenotype (the manifest characteristics of an organism). There is no neat mapping between the two. Non-fundamental characteristics (e.g., the pigmentation of human skin) are determined by two or more genes -- they are polygenic. Also one gene may play a rôle in shaping several characteristics -- they are pleiotropic, and so exert several influences on the phenotype. Kitcher (p.11) gives as an example genes which affect eye colour in the fruit fly Drosophila melanogaster and also drastically reduce the ability of the flies to mate.

16. Some scientists have stated that `it's all in the genes'. Richard Lewontin in The Doctrine of DNA, quotes, disdainfully, a leading molecular biologist who said that if he had a large enough computer and the complete DNA sequence of an organism, he could compute the whole anatomy, physiology and behaviour of that organism. But this is false. The characteristics of an organism are shaped by a history of complex interaction with the environment. [Lewontin's example, pp.63-4].

17. Most organisms consist of cells, and a cell generally contains a nucleus. In an organism, cells are constantly dividing and forming new cells, and during this process, chromosomes develop within the nucleus. It is these chromosomes which carry the genes. In the particular process, called meiosis in which sex cells (gametes) are formed, the number of chromosomes is halved, so that when mating occurs and a fertilized egg (zygote) is produced from the sperm (the male sex cell) and the ovum (the female sex cell), that fertized egg now has the regular number of chromosomes -- half contributed by the male parent, half by the female, which means that it receives half its genes from one parent, half from the other.

18. Chromosomes pair up, at meiosis, with morphologically similar mates and when the gametes are formed, each receives one chromosome from each pair. Each gamete has 23 chromosomes and, after fusion, the resulting zygote has 23 pairs. Each pair of chromosomes contain loci for the alleles. If a similar allele (say, for blue eyes) occurs on each chromosome at the same locus, then the individual will have blue eyes.

19. Evolution depends on genetic variation. How does such variation arise? One way is mutation which occurs before meiosis is complete. Mutation produces a mutant allele at a given locus on the chromosome.

20. Another way is through recombination when homologous chromosomes break and the broken bit rejoins not with the original part from which it was separated but with the counterpart section of its mate (see Kitcher's diagram on p.15). These recombinant chromosomes contain novel combinations of genes.

21. Research in the 1940s and 50s revealed that the genetic material in cellular organisms is deoxyribonucleic acid (DNA) and the structure of DNA was identified by Watson and Crick in 1953 (the double helix). Inside the double spiralling chain of sugar phosphate are `rungs' which are called bases or nucleotides. This was an important step towards understanding how genes contribute to the determining of phenotypical characteristics. Genes contain `information' controlling the formation of polypeptides, which are chains of amino acid.

22. These polypeptides combine together in complicated ways to make proteins. Phenotypical characteristics, such as eye colour, are the result of chemical reactions involving proteins. It is the order of the bases (the nucleotides) in the gene which constitutes the `information' for forming particular kinds of polypeptide. Thus the project of sequencing the genome consists of charting the constitution of each of the nucleotides.

23. Sometimes the order of the nucleotides in a strand of DNA gets changed -- a nucleotide may get deleted or replaced by a different one, or perhaps new nucleotides are inserted in the chain. This is known as a mutation and since the mutant gene contains information different from the original and (like all other segments of DNA) self-replicates, it can lead to an alteration of the phenotype (e.g.? albinos)

24. By comparing the structure of proteins in various species of animal, it is possible to perceive how a series of mutations served to transform one species into another. Thus we now have the means for giving a detailed, testable account of how such transformation occurs, an account which, of course, was not available to Darwin.

25. Modern evolutionary theory is a synthesis of Darwin's basic ideas with the mathematical theory of population genetics which developed in the 1930's. Given a population of organisms freely interbreeding, with the resulting emergence of new genotypes, it is possible to mathematically predict changes in the gene pool (the aggregate of the genotypes of a population) -- with some genes achieving higher incidence in the pool, and with the pool reaching equilibrium under various simple conditions. Of course, the mathematics becomes much more complicated when we factor in the effects of mutation, migration of alleles, changes in the environment which would entail that certain alelic combinations have an advantage.

26. The mathematics allows us to determine how many generations it takes for an allele which initially occurs rarely to become fixed in a population, in the sense that it becomes the only allele at a given locus (see Kitcher, p.19). Thus, if a certain allele or combination of alleles secures an advantage for organisms in a particular environment, then, given the fitness or selective value of that combination or genotype, we are able to predict mathematically the changes of frequency of that genotype or of a specific allelic combination over time. The maths is complex, because typically it is not the presence of one favourable allelic combination that secures a fitness advantage, but several in concert.

27. Merging Darwin's fundamental idea that changes in populations come about (principally) through natural selection with genetic theory, we can (following Kitcher, p.20) characterize a Darwinian theory of evolution: The most important evolutionary changes come about because some allelic pairs are fitter than others, and these obtain greater representation for their constituent alleles in subsequent generations.

28. If one is to defend the view that species evolve, one needs a clear notion of a species. Roughly speaking, two species are different if members of one do not interbreed with members of the other. This will usually be because of mechanical difficulties, or because of lack of sexual attraction, or because hybrids are sterile. How then does species separation (speciation) take place? The simple answer, suggested by Ernst Mayr, is that initially there is a geographical separation -- a portion of the species becomes physically separated from the rest. If the geographical environments in which the two groups live are (or become) different, then natural selection may ensure different genotypical developments for the two populations, so that, in the end, they become so different that, even if they were put together again, interbreeding between members of Group A and Group B could not occur.

29. A new species can also come into existence simply because, after many generations of change, the later genotype is so different from the earlier that if per impossibile a member of the old generation attemped to breed with a member of the new, he couldn't.

30. A similar explanation for the emergence of a new species, applies to the emergence of new genera, families, orders, classes, phyla. For example, a species may develop in such a way as to allow it to enter a previously uninhabited adaptive zone. This then, in outline (and following Kitcher) is the Theory of Evolution, and it is this theory to which Creationism stands opposed – not just in the sense of saying that it is wrong, but in providing an alternative account of the undisputed phenomena.

31. Creationism is spreading: “… the US is the world’s leading scientific nation. Yet 47% of Americans – and a quarter of college graduates – believe humans did not evolve but were created by God a few thousand years ago. Nearly a third believe Creationism should be taught in science lessons” (New Scientist 14/12/2000; see http://www.newscientist.com/creationism/features_22352.html

32. One common accusation is that evolutionary theory is not proven and therefore has no scientific status. So, say Creationists, believing in evolution is just a matter of faith -- and why should we prefer children to accept this faith rather than religious faith? The answer to this is that, although most of the truths of science have not been proven beyond all possible doubt, nevertheless many of them have been subjected to repeated testing and have survived. There is a world of difference between believing a theory for which we lack conclusive proof and just accepting some unfounded claim. The whole history of science is testimony to human fallibility, yet there is nothing unreasonable in believing to be true a theory for which we have overwhelming (but not conclusive) evidence. Against Creationists' claim for parity, Kitcher observes that `all theories are revisable, but not all theories are equal' (p.34).

33. Creationists charge evolutionary theory with predictive failure. This charge can come in three varieties, which Kitcher usefully distinguishes. Perhaps the favourite ploy is to adopt Popper's criterion of falsifiability and to argue that evolutionary theory is unfalsifiable and therefore unscientific. Kitcher provides a demonstration that the unrefined Popperian view on which Creationists rely is untenable. The reason is that, if we come across what seems to be a predictive failure of a certain theory, we can always say that some unforeseen force was at work to produce that unexpected result. Hence any theory is unfalsifiable. One could object to Kitcher that the ad hoc importation of mysterious `forces’ is not scientifically respectable. Yet, in the history of science auxiliary hypotheses have sometimes been introduced to `save’ certain well-established theories, so Popper, it seems, must at least confront the question of deciding when importing an hypothesis is a desperate and unacceptable attempt to `immunize’ a theory from falsification and when it is a respectable and legitimate measure. For further criticisms of Popper, see Max’ recent lectures.

34. In defence of a Popperian account, could we point out that hypotheses are not falsified singly, but come embedded with a lot of other assumptions, and that the whole bundle of statements does have observable consequences so that evolutionary theory, considered this way, is falsifiable and hence respectable? The trouble with this way out is that, by adding assumptions to any statement, however crazy or nonsensical, one can produce a bundle with testable, i.e. falsifiable consequences. So the criterion is too slack: it allows us to count nonsense as scientific. So this kind of falsificationism -- which Kitcher calls `naive falsificationism' is useless. Therefore Creationists are unwise to wield naive falsificationism against evolutionary theory, since that criterion can show that any science is not a science; hence it is that criterion that is at fault. Of course, the corollary to this, as Kitcher notes (p.44), is that scientists should not use the criterion of naive falsificationism as a means of rejecting Creation Science as unscientific.

35. By considering the example of Newtonian mechanics, Kitcher identifies certain criteria for a successful science: independent testability, unification and fecundity (p.48). In other words, there is much more to successful science than the making of predictions; what we require also is the furnishing of explanations. So the question is `Does evolutionary theory satisfy the above criteria for being good science?'

36. Kitcher answers `Yes'. If we want to know, for example, why a contemporary creature possesses a certain trait, we supply a Darwinian history which describes how that trait emerged. Similarly, to find out why two species share a particular trait, we may trace their descent from a common ancestor. We can explain why certain species became extinct by showing how characteristics that were beneficial to their survival were no longer effective when a change of environment or a change of competition occurred.

37. Kitcher 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 carnivorous 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. (For a nice example of how an evolutionary phenomenon – the development of trichromatic vision in primates – meshes with work in palaeontology and molecular biology, see `New Fossils and a Glimpse of Evolution’, Science 295 (25 January, 2002) at www.sciencemag.org Some of this work was done in the Anatomy Department of HKU.) Darwin himself acknowledged that there were many questions to which he did not have the answers, but he initiated a research programme, and many of the answers to those questions are now known. His theory spawned other areas of enquiry (such as sociobiology). In short, the theory satisfies our criteria for good science.