Book Review: Why Evolution is True

If you have never heard of sexual selection, if "evo-devo" sounds like the name of an 80's new wave band, if you believe in evolution but don't understand it, Jerry Coyne's forthcoming book Why Evolution is True isn't a bad place to kick off your intellectual journey. There is no one book that can encompass everything that is important to understand about evolution, but Why Evolution is True makes an admirable attempt at surveying the intertwining lines of evidence scientists follow to determine how life came to be as it is. Indeed, Coyne's book follows in the long tradition of popular books that have plainly expounded upon the basics of evolution by natural selection, working as a primer and a road-map for those with an interest but not much background. Paired with Donald Prothero's fossil-oriented survey, Evolution: What the Fossils Say and Why it Matters, Coyne's book can be a useful resource to the general reader.

If you are already familiar with the basics of evolution, though, the book does not present much that is novel, and it might be better to pass it up to slog through familiar explanations of evolution involving Tiktaalik, widowbirds, bacterial resistance, etc. Worse, the book is not only a little bland, but it is pockmarked by a series of small errors and failures to convincingly marshal the available evidence in favor of evolution. For the purposes of this review, I will stick to the areas in which I have experience; the fossil record and the history of science.

First, the fossil record. Early in the chapter, "Written in the Rocks," Coyne states that in order for a fossil to be formed, the remains of an animal must find their way into water and become buried, after which they are mineralized over time. Fossils can form this way, but it is not the only way that fossils can form, nor are all fossils bones. Fossils may be bones, footprints, body impressions, coprolites, feathers, armor, teeth, insects in amber, burrows, shells, etc. Generally, they are the preserved traces of ancient life, and preservation will differ in different environments. An insect can be stuck in sap which turns to amber, a mammal could die in a hollow treetrunk filled with sediment and debris, or a nesting dinosaur could be buried in sand or mud. There is no one way to make a fossil. Perhaps this is nitpicking, but I think that Coyne's treatment of fossil formation leaves far too much out. This is a recurring theme in the chapter.

Rather than chronologically surveying the whole of vertebrate evolution (the traditional method, exemplified by Prothero's book, Colbert's Evolution of the Vertebrates, and Richard Fortey's Life), Coyne selects a handful of transitions to make his case. In a move that annoyed me throughout the book, Coyne calls these fossils "Missing Links." I wanted to strike the phrase out every time I saw it. The term "missing link" is associated with the Great Chain of Being, or a ranked order of nature from lower (inferior) to higher (superior). Even though this idea has fallen out of fashion as an organizing concept for life and the pattern of evolution, it still remains in our explanations and illustrations. On page 50, for instance, a phylogeny of whales is provided to illustrate whale evolution. It is a branching diagram, that is true, but what is meant to catch the eye are the illustrations showing a terrestrial creature on the bottom and a baleen whale on the top, a straight-line progression from one point to another. We complain when people say they think evolution is goal-oriented, but in our illustrations (which can be more influential than the text), we are still supporting "Chain thinking."

The first group of transitional forms to be covered are early tetrapods, in the subsection "Onto the Land: From Fish to Amphibians." Tiktaalik is the star of this section, to the detriment of other genera. The story of Tiktaalik is a good one, particularly how a search was mounted to test an evolutionary prediction, but not enough information is provided about the evolutionary bookends on either side of the famous fishapod. Coyne says that there were terrestrial tetrapods on the one side and fish on the other, but essentially no details are given about them (in an illustration, Eusthenopteron is chosen as the fish and Acanthostega is chosen as the tetrapod, with Tiktaalik in between).

As pointed out in a new review by Coates et al. on early tetrapods, though, there was not only a diversity of early tetrapods, but two radiations of animals important to understanding the evolution of the group. Likewise, limbs evolved in the water and were then used to move about on land, but Coyne repeats the standard trope about the evolution of limbs and the "invasion of the land." I can't hold him accountable for a review published after his book was printed, of course, but the information in the Coates et al review is not new, and there have been other reviews of early tetrapods (like Jennifer Clack's Gaining Ground) that could have helped flesh out the story.

Next up is the evolution of birds, which leads to something of a contradiction. Coyne starts off by stating that "if you think about it a bit, it's not so hard to come up with intermediate stages in the evolution of flight, stages that might have been useful to their possessors. Gliding is the first obvious step. And gliding had evolved independently many times: in placental mammals, marsupials, and even lizards." For the evolution of birds, this would mean a "trees down" origin for flight. Later in the chapter, though, Coyne states that the "ground up" scenario is more likely, which makes the opening statements of the section peculiar.

Nevertheless, this section is like the last in that sparingly few feathered dinosaurs and early birds are mentioned. Archaeopteryx is the star, but Coyne makes a mistake when he states "After the discovery of Archaeopteryx, no other reptile-bird intermediates were found for many years, leaving a gaping hole between modern birds and their ancestors." This ignores the many papers T.H. Huxley devoted to the problem of bird origins, as well as consensus that birds had evolved from "pseudosuchians" akin to Ornithosuchus and Euparkeria until just a few decades ago. It is curious why this point was left out, particularly since it is illustrative of the way in which science works! Instead, Coyne gives us the impression that we are simply waiting fore new fossils at which time the scales will fall from our eyes and all will be understood. Sinornithosaurus, Microraptor, and Mei long all receive brief mention, but the evolution of feathers and the fact that feathers are a feature of coelurosaurs (including tyrannosauroids like Dilong) are subjects that apparently didn't make it in. Coyne lays out the fossils in sequence, but he does not convincingly draw them together and explain how birds evolved.

Third is the evolution of whales, and this section follows the pattern of the previous two. It is not mentioned how we know each of the transitional forms, like Pakicetus and Ambulocetus, are whales, only that they are and fit in sequence. Following that sequence, Coyne mentions Dorudon and Basilosaurus, which he says had "blowholes atop the skull." This is false. These creatures still had nostrils near the front of their snouts, and even in later forms like the tooth-and-baleen-bearing Aetiocetus the nostrils were still placed in front of the eyes even though they had been move backward. In fact, I am puzzled by why Coyne jumps from Dorudon to modern baleen whales as if there are no more transitional forms (like Aetiocetus). A brief acquaintance with the literature on the subject shows that there is more to the story than Coyne is telling. We are again subjected to a standard account that not only contains a few errors, but fails to convincingly explain how whales went from being terrestrial to aquatic.

I will now jump to the penultimate chapter, the one concerned with fossil hominins. Coyne picks up with the discovery of the "Taung child,"Australopithecus africanus in 1924. Coyne says that this was the first "stepping stone" to understand our own origins. This is false. The debates over "Pithecanthropus erectus" (later Homo erectus) from Java, the Neanderthals, and the Piltdown fossils illustrated the search for our ancestors, whether those ancestors existed among the apes or some kind of "Eohomo." Coyne mentions some of these finds, but apparently did not dig deeply enough into the debates over them. (Piltdown doesn't even garner a mention. This is unfortunate. Yes, it gave science a black eye, but better to acknowledge it and confront it than ignore it due to discomfort.) Even when Dart described Australopithecus africanus in 1925, many of his colleagues thought it was a fossil ape and not directly relevant to the origin of our species. The story is more complex than I cannot do justice to here, but suffice it to say that Australopithecus did not get its come-uppance until W.E. le Gros Clark rehabilitated it in the late 1940's after examining the original fossils himself.

Coyne also repeats a brief summary of the 1925 Scopes Trial seen earlier in the book. He says "In the famous 'Monkey Trial' of 1925, high school teacher John Scopes went on trial in Dayton, Tennessee - and was convicted - for violating Tennessee's Butler Act." This is a gross oversimplification designed to make Scopes out to be a martyr for science. In truth, the trial was hatched as a publicity stunt, concocted by local businessmen who took up the ACLU's offer to make a test case against the Butler Act. Scopes was a substitute teacher for a biology class once and was not even sure he mentioned anything at all about evolution. He volunteered to be the victim, and while found guilty, was just a part of a circus that, despite many historical treatments (see Edward Larson's Trial and Error for the short version and Summer for the Gods for the long one), people still misunderstand. Either Coyne simply rehashed textbook cardboard or refused to acknowledge the actual historical events to make his point.

A curious label also appears on page 197. In an illustration of the ages in which hominins lived, there are labels for A. rudolfensis and A. habilis. These are Homo rudolfensis and Homo habilis, and Homo habilis is referred to in the text. Some think that H. habilis should be grouped within Australopithecus, but no reason for or against this view is presented in the book. It is a minor slip in consistency, but I had to wonder why it was not caught.

Also curious is Coyne's question "What, then, propelled the evolution of humans?" This makes it sound as if there were only one reason for our evolution, or that it was deigned to be (we were "propelled" toward our present state by an ancient change). By "human," do we mean the genus Homo, or perhaps hominins in general? Were there not different selective pressures at different times? To his credit, Coyne does point out that evolution is a branching process multiple times, but the concept of evolution towards a particular end still creeps in around the edges.

There is a lot more that I could complain about, but I think I have already gone on for too long. Why Evolution is True is not a bad book, but it is riddled with little errors and oversimplifications. In terms of the content dealing with fossils, transitional forms are paraded out but their connections to one another are generally not illuminated. Precisely how early tetrapods were derived from lobe-finned fish or birds from feathered dinosaurs is not explained, and so Why Evolution is True fosters belief in evolution but falls short when it comes to cultivating understanding.

I'm sure that some will say that I'm being overly harsh on this book, and that may be true. I have reason to be. Over the past two years, as I have been working on my own book, I have spent many hours pouring over papers and books trying to learn about evolution. When I consider the evolution of whales, for instance, I do not simply want to know the names of the animals but how they differ, why they differ, and what that says about how whales evolved. It frustrates me, then, to see an author rehash popular summaries but essentially ignore the details, which are readily available in the literature. It seems that the treatments of transitional fossils in Why Evolution is True were gleaned from readily available popular summaries and there was little actual research that went into these sections.

For a particular audience, Why Evolution is True can be a useful book. If you don't know much about evolution, but have a craving to know more, it would not be a bad starting place. Otherwise, there's little that distinguishes it from other popular books that seek to summarize evolution; if you have read one, you've generally read them all.