Monday, 5 July 2010

Why Evolution is True – Jerry A. Coyne ****

There is no shortage of books about evolution, but few of them tackle the question of proof as directly as this one, and perhaps none of their authors do so in such an accessible way as Jerry Coyne. The result is a thorough, even-tempered and plain-spoken summary of the evidence for evolution by natural selection. Some glitches appear when Coyne strays from a simple catalogue of the material evidence for evolution, but on the whole the book is convincing.
Coyne sets a clear target in the first 40 pages. The problem, as he puts it, is a “simple lack of awareness of the weight and variety of evidence” in favour of evolution. Next he distinguishes six tenets of evolutionary theory: change of species over time, gradualism, speciation, common ancestry, natural selection, and mechanisms other than natural selection.
Readers may find it awkward that this six-fold distinction is not reflected in the structure of the rest of the book: the chapters are organised by the source of evidence for evolution (fossil record, biogeography, embryology, human evolution, and so on) rather than the six hypotheses that are the target of this evidence. But with his six tenets Coyne does a good job of untangling some of the conceptual knots surrounding Darwinian evolution.
The meat of the book is seven chapters on the evidence for evolution. For each of Coyne’s arguments and case studies, there will be many readers who, with a solid interest in evolution but no formal training, have seen those arguments and case studies before. But there will be few lay readers who will be familiar with all or even most of them. The value of the book is that it collects a wide range of standard pieces of evidence in one place.
Structure-wise, some neat work is Coyne’s chapter entitled “Remnants”, which deals in one blow with vestigial traits, atavistic traits, embryology, and bad design. This is a smart way to package an array of evidence that could easily be confusing, or rendered overly complex, if it were scattered through the book. The decision to devote a chapter to human evolution is also a good one, since it addresses a psychologically compelling objection to Darwinism – that it seems impossible that humans in all their complexity evolved from the ancestors of monkeys.
Argument-wise, Coyne knows that a single example is rarely convincing, and leaves readers in no doubt about the quantity of evidence that supports each of the many lines of argument. To take just one case: as evidence for evolution by natural selection, the example of the peacocks tail is striking; but the fact that 232 experiments in 186 species indicate sexual selection is overwhelming.
The book’s main drawback is that Coyne spends so much time describing the evidence for evolution that he sometimes forgets to check whether that evidence distinguishes between evolutionary theory and alternative theories, especially creationism. A common pattern of argument in the book is that creationism can only accommodate the facts by arguing that God has arranged the facts to make it look as if evolutionary theory is true – an accommodation which, as Coyne argues, would be absurdly ad-hoc.
This argument works well with embryology, vestigial organs, and the fossil record, but less so in other cases. Evolution has a good explanation for the existence of different species, with the same survival functions, in different parts of the world. Creationism doesn’t have a built-in explanation for this, but it is not much of a stretch to suppose that the Creator just happened to make things this way. Likewise for the existence of fibrinogen – a protein used in blood-clotting – before it was deployed to help clot blood (in sea cucumbers). Evolution predicts this, Coyne argues, since it cannot build a complex process like blood-clotting from scratch. But it is not asking too much to suppose that the Creator used fibrinogen more than once in evolutionary history.
One conceptual quibble is that Coyne insists on calling evolution a “fact”, despite the common distinction between “facts” as directly observable states of affairs in the world, and “theories” as general statements that are inferred from the facts. Coyne implies that evolutionary theory is not a “fact” in this standard sense when he describes how the theory is confirmed – it is confirmed not by checking its truth against nature but by deducing predictions from it, and then checking the truth of those predictions against nature. This may just be a linguistic issue, but it’s better not to add fuel to the sceptic’s fire, however spurious the fuel might be. Why not just call evolution a “true theory”?
Another weakness is that Coyne ignores debates within biology about the nature and status of natural selection. He notes that debates exist about the details of how evolution occurred, and the relative roles of various evolutionary mechanisms (especially genetic drift). But the claim that biologists disagree about evolution is such a common one among sceptics that a few more pages – even a chapter – on the significance of these disagreements would have been useful.
Lastly there is the book’s jacket-cover claim that evolution is “a fact we should embrace without fear.” In the last chapter Coyne argues against the view that accepting evolution means endorsing immoral behaviour in present-day humans. He rolls out some standard arguments: the theory of evolution has no moral consequences because it is a scientific theory; many European countries embrace evolution but have not slipped morally; moral codes are stricter now than they have ever been; and we have other sources of meaning such as work, family, literature and science. All promising arguments, but they are too briefly delivered to convince anyone who does not already agree with Coyne on the issue.
Coyne writes that “every fact that has something to do with evolution confirms its truth.” This is surely an exaggeration, but Coyne summarises many of the facts that do confirm the theory of evolution, and does so in a way that any reader – whether or not they have a prior interest in biology – can grasp. Not all of his arguments work against creationism, but most of them do. Any evolution sceptic who reads this book, and is not tempted to change their view, is either dishonest or has not read the book properly.
Also on Kindle:  
Review by Michael Bycroft

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