Why Darwin? - an essay (review of books) by Richard Lewontin.

[Jim__]

Lewontin is a well-known American biologist. In the current version of the New York Review of Books, he has a somewhat long essay that discusses a number of current books on evolution. The most surprising part of the essay to me is where he states that natural selection is not certain to be the driving force behind evolution:

Coyne is an evolutionary biologist who, like his former student H. Allen Orr, has been a leader in our understanding of the genetic changes that occur when species are formed. His primary object in writing this book is to present the incontrovertible evidence that evolution is a physical fact of the history of life on earth. In referring to the theory of evolution he makes it clear that we do not mean the weak sense of "theory," an ingenious tentative mental construct that might or might not be objectively true, but the strong sense of a coherent set of true assertions about physical reality. In this he is entirely successful.

Where he is less successful, as all other commentators have been, is in his insistence that the evidence for natural selection as the driving force of evolution is of the same inferential strength as the evidence that evolution has occurred. So, for example, he gives the game away by writing that when we examine a sequence of changes in the fossil record, we can

determine whether the sequences of changes at least conform to a step-by-step adaptive process. And in every case, we can find at least a feasible Darwinian explanation.

But to say that some example is not falsification of a theory because we can always "find" (invent) a feasible explanation says more about the flexibility of the theory and the ingenuity of its supporters than it says about physical nature. Indeed in his later discussion of theories of behavioral evolution he becomes appropriately skeptical when he writes that

imaginative reconstructions of how things might have evolved are not science; they are stories.

While this is a perfectly good argument against those who claim that there are things that are so complex that evolutionary biology cannot explain them, it allows evolutionary "theory" to fall back into the category of being reasonable but not an incontrovertible material fact.

There is, of course, nothing that Coyne can do about the situation. There are different modes of "knowing," and we "know" that evolution has, in fact, occurred in a stronger sense than we "know" that some sequence of evolutionary change has been the result of natural selection. Despite these misgivings, it is the case that Coyne's book is the best general explication of evolution that I know of and deserves its success as a best seller.

Is Lewontin's opinion about the uncertainty of natural selection as the driving force behind evolution in line with the opinion of most contemporary biologists?

[drm604]

1. I'm not a biologist and I certainly haven't done an extensive review of the current literature

but I have the strong impression that his opinion is not in line with most contemporary biologists. Certainly there is discussion about things like genetic drift being an important factor in speciation but, at least in my non-biologist opinion, that's not the same as saying that it's a bigger force in overall evolution than natural selection.

[Odin2005]

2. Lewontin is a Marxist ideologue who lets his political beliefs compromise his objectivity.

And his opinions are certainly NOT in line with those of most biologists.

[Jim__]

3. Claims about his politics do nothing to address his scientific claims.

And, he has certainly earned the right to express his opinion on questions of biology (Lewontin):

Lewontin has worked in both theoretical and experimental population genetics. A hallmark of his work has been an interest in new technology. He was the first person to do a computer simulation of the behavior of a single locus (previous simulation work having been of models with multiple loci). In 1960 he and Ken-Ichi Kojima were the first population geneticists to give the equations for change of haplotype frequencies with interacting natural selection at two loci.<1> This set off a wave of theoretical work on two-locus selection in the 1960s and 1970s. Their paper gave a theoretical derivation of the equilibria expected, and also investigated the dynamics of the model by computer iteration. Lewontin later introduced the D' measure of linkage disequilibrium.<2> (An achievement that he would be less happy to claim is that he introduced the name "linkage disequilibrium" itself, one about which many population geneticists have been unenthusiastic).

In 1966, he and Jack Hubby published a paper that revolutionized population genetics.<3> They used protein gel electrophoresis to survey dozens of loci in Drosophila pseudoobscura, and reported that a large fraction of the loci were polymorphic, and that at the average locus there was about a 15% chance that the individual was heterozygous. (Harry Harris reported similar results for humans at about the same time).<4> Previous work with gel electrophoresis had been reports of variation in single loci and did not give any sense of how common variation was.

Lewontin and Hubby's paper also discussed the possible explanation of the high levels of variability by either balancing selection or neutral mutation. Although they did not commit themselves to advocating neutrality, this was the first clear statement of the neutral theory for levels of variability within species. Lewontin and Hubby's paper had great impact -- the discovery of high levels of molecular variability gave population geneticists ample material to work on, and gave them access to variation at single loci. The possible theoretical explanations of this rampant polymorphism became the focus of most population genetics work thereafter. Martin Kreitman was later to do a pioneering survey of population-level variability in DNA sequences while a Ph.D. student in Lewontin's lab.<5>

etc.

And if he is neither misquoting nor misrepresenting Coyne in this statement:

(We can) determine whether the sequences of changes at least conform to a step-by-step adaptive process. And in every case, we can find at least a feasible Darwinian explanation.

Then he makes a fair demonstration for his claim:

There are different modes of "knowing," and we "know" that evolution has, in fact, occurred in a stronger sense than we "know" that some sequence of evolutionary change has been the result of natural selection.