There is a conversation about evolution that I’m apparently doomed to replay over and over with various family members, friends and acquaintances.

I tell a friend that the evidence for evolution is overwhelming - everywhere in biology you find the signature of evolution; in every little bizzare, unexpected nook of biology you find unmistakeable evidence that all life is related, descended from common ancestors that lived long ago and took forms that were very different from what we observe in today’s organisms. We swim in a deluge of evidence, and I’m baffled that anyone can disregard the pervasive stamp of evolution in nature.

Whoever I’m having this conversation with is equally baffled. How can I look around at the unparalleled complexity of nature, at the amazing adaptations possessed by millions of species, and think that this all came about through an unintelligent process?

To end this mutual bewilderment between biologists and the 45% of the US population that doesn’t accept evolution, we need readable, friendly books that explain why biologists think the way they do. Jerry Coyne steps into the gap with a straightforward introduction to the wide-ranging findings from disparate fields of biology that solidly support the modern theory of evolution.

As the no-nonsense title suggests, Why Evolution is True lays out, in plain language, the basic ideas behind evolution and the types of evidence that support these ideas. Coyne takes a reader on a tour of paleontology, evo-devo, biogeography, natural selection and genetic drift, sexual selection, and his own professional specialty, speciation. He finishes up with a chapter on the one evolutionary branch that most us find more interesting than any other, that is, our own, and with the always obligatory chapter laying to rest the ill-founded but widespread concerns that our children will fall into an uncivilized, Hobbesian state if they’re taught that they descended from monkeys and slime.

Coyne’s book has several distinct advantages over many other books in the pop-evolution genre. For one, he’s conversational, which makes the book an easy read. Learning the basics of evolution, doesn’t have to be hard, and Coyne makes it fun. Coyne may not be a prose stylist like Richard Dawkins or Stephen Gould, but his clear thinking is accompanied by clear writing. Occasionally I thought that Coyne assumed more background knowledge that most readers might have (I wish more people knew what igneous rocks and amino acids are, but most readers probably don’t), however, with an occasional trip to Wikipedia, any literate, interested reader will do fine.

Coyne’s clear style is supported by an effective explanatory strategy. In the first chapter, he lays out some main principles of evolution:

1) evolution is gradual change over often long periods of time, resulting in organisms that can be very different from their ancestors;

2) evolution is gradual - dogs don’t give birth to cats, lizards don’t give birth to chickens; even rapid evolutionary change is gradual by any human understanding of the term;

3) new species often arise by the splitting of genealogical branches, which means that;

4) today’s living species have descended from common ancestors;

5) natural selection acting on variation is responsible for producing organisms that are highly adapted to their environment, and;

6) other processes, like genetic drift, shape evolutionary trajectories.

From general principles like these, Coyne demonstrates that scientists can make predictions about what we expect to find in nature. For example, evolutionary theory suggests that there will be a predictable evolutionary succession of fossils. Whales have certain features that make us suspect that they descended from land-dwelling mammals; so we expect to see a transition from land to sea animals in the fossil record, which we do see. If land-dwelling vertebrates evolved from fish ancestors, we should be able to find fossils of fish-like animals with primitive limbs, which we do find.

In each chapter, Coyne lays out evolutionary predictions, and then uses well-chosen examples to show how those predictions are confirmed.

Coyne then takes the argument one step further. Evolution generates clear expectations of what we should find in nature, while creationism can only explain nature by appealing to arbitrary, inscrutable decisions made by an inaccessible designer. Certainly an omnipotent designer could have chosen to make the world this way, but creationists have no testable explanation for why the designer chose to do it one way, instead of another. Thus, intelligent design advocate Michael Behe ascribes a peacock’s tail to a designer’s whimsy, while biologists say the tail is the result of sexual selection. Behe’s idea is arbitrary; biologists’ claims flow naturally from evolutionary theory. Behe’s idea can’t be tested; biologists have tested theirs.

While underscoring the intellectual bankruptcy of a design explanation, Coyne wisely steers clear of an outright attack on religion, and in fact he hardly spends any time at all refuting specific arguments of creationists. This book is not a take-down of creationism; it’s a primer on evolution intended for a broad audience. Coyne is interested in science, and leaves readers free to draw their own religious conclusions, which is exactly how this issue is also treated in professional science circles. Scientists agree on the science, and differ with each other over religion.

The book finishes up with an interesting discussion of the common worry that teaching evolution to our kids will unleash “the beast within.” (I don’t know about you, but it doesn’t take evolution to unleash the beast within my kids - it pretty much starts out unleashed.) Instead of just rattling off a few bromides about how science doesn’t have to tell us how to act, Coyne takes on some of the ideas of evolutionary psychology and the idea of genetic determinism.

If we’ve evolved a certain way, do we have to be that way? No - just because something’s genetic, doesn’t mean you can’t modify it. The most commonly used example of this idea is eyesight: Coyne’s poor eyesight (and mine) is the result of genetics, yet it’s 100% fixable with an environmental change, a pair of glasses. Some genetic traits are more susceptible to environmental change than others, but the point stands: genes aren’t the same thing as destiny.

We’ve long needed more engaging, readable, non-polemical books that provide a general overview of why biologists think about evolution the way they do. Should I find myself again engaged with a friend who is baffled that I think the evidence for evolution is overwhelming, Why Evolution is True will be the first book I recommend.

Why Evolution is True
by Jerry A. Coyne
Viking, 2009

Front page image of T. Rex courtesy the Wikimedia Commons.