Why Evolution Is True

Understanding science is hard for non-scientists because of the technicalities involved, especially the mathematics. But no intellectually responsible non- scientist can get away with ignorance about the sciences, which collectively constitute humanity's greatest achievement. There is no excuse for lacking at least a broad-brush sense of what is happening in fundamental physics, cosmology and biology -- just to take the major areas of contemporary interest -- not least because there are so many good books for the general reader by first-rate practitioners in these fields.

A paradigm case is Jerry Coyne's lucidly brilliant account of evolutionary theory, Why Evolution Is True. For many reasons, among them the rapid advances we are witnessing in contemporary biological science, an understanding of evolution as the central principle of biology is crucial. If we are to be informed participants in the debate about what we want from the applied biological sciences, across the range from medicine to cloning to genetic modification of crops to the saving of endangered species, we need a proper understanding of evolution as the living world's organising principle.

Everyone who reads Coyne's book with attention will acquire this understanding. It is a model of expository clarity and intellectual rigour, a point for other science writers to note; all that readers need note is how accessible it is, and how fascinating. Moreover in it Coyne carefully and conclusively refutes efforts by "intelligent design" creationists to contest evolutionary biology. This, given the state of the debate over biology, is by no means the least important aspect of his book.

Religion-motivated efforts to derail serious biological enquiry, and therefore to interfere with responsible science education, are worse than merely a time-and-energy wasting distraction. They arise in connection with all three of the main nodes of contention between religious and non-religious outlooks in today's society. One is the question of the intrinsic credibility of the claims made by revealed religions, another is the question of how much influence religious viewpoints should have in the public square, and the third is the overall question of the relation between religion and science.

In this last domain two different, indeed inconsistent, strategies are open to religious apologists, some of whom nevertheless combine them. One is to say that religion and science speak different kinds of truth because they address different realities, the spiritual and material. The other is to say that religion and science are direct competitors for the truth about the one and only reality, namely, this world; which is what creationists claim.

An ability to embrace contradiction in a non-Hegelian way (for an Hegelian, contradictions always disappear by resolving into new syntheses) is a specialty of the religious mindset. Thus in their recently-published book Questions of Truth Nicholas Beale and physicist-turned-preacher John Polkinghorne are able to defend a form of Episcopalian Christianity by nominating some bits of the Bible as symbolic and others as literally true, in order to diminish the points of conflict between Biblical accounts and science, and then by making standard "god of the gaps" and "argument to the best explanation" moves, which in a nutshell come down to saying "we don't understand this so let's say Fred did it" ("Fred" is my name for any suppositious supernatural agency defined ad hoc for some purpose religionists have in mind).

Creationists in their disguise as "intelligent design" (ID) theorists are squarely in the camp of treating religion and science as direct competitors. They claim that nature contains "irreducibly complex" phenomena which can only be explained by invoking a designer, on the grounds that they cannot have arisen through non-purposive processes acting on simpler elements.

Coyne and anyone else could offer a short answer to this: that it is a version of the Fred arguments just mentioned, in that if it were true that one cannot see how some complex thing came to be, it is better to keep looking for the explanation -- or even to accept the one does not know the answer -- than to take the gigantic leap to the profoundly implausible quick-fix of claiming that some putative Fred did it. The reason that ID theorists invoke a Fred is that they have other and prior reasons for wanting Fred in the picture -- mainly, to keep us observing their preferred version of morality, and paying our tithes.

But Coyne does not take this easy option, even though it is right. He does another right thing, which is to walk us, in painstaking and illuminating fashion, through the evidence for biological evolution, and to display the failure of the "intelligent design" case in comparison.

We accordingly see the mountains of evidence for evolution from fossils, embryology, biogeography, transitional forms, the formation of new species both in the fossil record and in real time with natural selection observably in action, the existence of vestigial structures (the human appendix, for example), dead genes, and suboptimal organisation (if there were a designer, this would be evidence for incompetence, sometimes gross). And evolutionary theory makes testable predictions: biologists can predict where (in place and period) fossils will be found, in particular when in the evolutionary story shared ancestors will fit in and what they will be like; and what characteristics species will have if they have certain other characteristics -- for example, if an animal species has brightly coloured males and drab females, one can predict that it will have a polygonous mating system.

What all these lines of enquiry overwhelmingly attest is yet further supported by genetics. "DNA sequencing supports the evolutionary relationships of species originally deduced from the fossil record?Every fossil that we find," writes Coyne, "every DNA molecule that we sequence, every organ system that we dissect supports the idea that species evolved from common ancestors." And it is not only what we do find but what we do not find that provides support: "We don't find mammals in Precambrian rocks, humans in the same layers as dinosaurs, or any other fossils out of evolutionary order."

Even though it is not the only mechanism of evolutionary adaptation, natural selection is by far the most important. Coyne devotes many pages to marshalling the evidence for it. A simple example is the fur colour of wild mice. Mice that live on dark soil have dark fur, mice that live on pale soil have light fur. Experiments have shown how quickly mice populations can adapt to the colour of their home soil. A research team at Kansas University built large outdoor enclosures and populated them with mice, some with dark and some with light fur. The mice whose fur more closely matched the soil survived owl predation better than those whose fur did not camouflage them. The former bred more, and soon the population as a whole had fur closer in colour to the soil.

What had happened was that natural selection had operated on the distribution of genes for fur colour, increasing the frequency of those variants that made for survival-enhancing fur colour and hence greater chances of reproduction. "There is no will involved, no conscious striving," Coyne points out; adaptation is inevitable and automatic in the circumstances.

And more to the point, the mechanism of adaptation is fully sufficient for the emergence of complexity from simpler elements. The increasing elaboration of anatomical traits is clear to see in the fossil record. Biochemical pathways do not fossilize, so here the detective work is more intriguing: such cases as blood clotting (a sixteen step process) and the several times that eyes have separately evolved in different parts of the animal kingdom, can be reconstructed step by step. Coyne gives examples -- in the case of eyes, starting with the light-sensitive pigments seen in flatworms and going through the increasingly more sophisticated versions of precursor eyes respectively in limpets, the chambered nautilus, ragworms, abalones, and so upward - showing how every stage of the process confers some evolutionary advantage in the way of finding food, avoiding predators, and/or reproduction. Moreover he reminds us of the huge lengths of time and the billions of failures that contribute to the evolutionary story too.

Coyne shows science carefully, responsibly, testably, profoundly at work on the glory that is the natural world. It starts with no prejudices (it is not trying to prove that there is no Fred, having decided at the outset that this is its aim), but is open and self-critical. What you see in Coyne's account is science as the enterprise that seeks to understand, and always stands ready to revise itself in the face of contrary evidence. It is a beautiful process, and the results are literally wonderful. Coyne's book is a testament to this. It seems almost coincidental to say that it is also a brilliant introduction to evolution which should be required reading: in its blaze of illumination the ID case melts like summer snow.

About the Columnist
A. C. Grayling is an author, playwright, reviewer, cultural journalist, and professor of philosophy at London University. The most recent of his many books are Towards the Light of Liberty and The Choice of Hercules. His play Grace was recently performed in New York City.

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