When I was reading Richard Dawkins’ new book, The Greatest Show on Earth: The Evidence for Evolution (Free Press, 2009), a few weeks back, I 
took pretty careful notes. I did this so that I could always have some quick reference to the evidence Dawkins offers, and so that when at some later point I chose to “review” the book, I’d have a better recollection of its strengths and weaknesses.
I’m now inclined to pen a few comments on the work, and to summarize–very, very briefly–a few of the many lines of evidence that Dawkins offers in support of this important yet savagely maligned scientific theorum (“theorum” being Dawkins’ own neologism, coined to suggest a factually stronger set of data and inferences than a simple theory, although truthfully, in the scientific sense, a theory is more or less tantamount to fact, a detail that scientists and defenders of science often must pain themselves to explain to denialists and other anti-science types who resort to the hackneyed “it’s-just-a-theory!” argument).
This book is an extremely valuable contribution to the public discourse on evolution. For far too long (IMHO) there has been a lack of accessible, layperson-friendly information on the positive evidence for evolution. It seems that all too often, scientists and science advocates have to be continuously on the defensive; they must spend the majority of their time combatting creationist criticisms of Darwin’s theory of origins. As a result, dialogue pertaining to the actual scientific data that establishes evolution as a theory/fact as solid as any in science, is stifled, sidelined, and marginalized. This is ironic, because if more people were willing to listen to these evidences in the first place, the many ignorant, vacuous, creationist canards that are perpetually regurgitated in critique of evolutionary theory, would most likely be preempted. Dawkins has done a great service to science and to public understanding thereof by taking the time to boldly advance the experimental, observational, and theoretical data that has established evolution as the single best explicatory model of biological diversity that has ever been developed. Hopefully the dialectical contribution represented by this book will help assert and (re-)establish in the public sphere evolution’s position as recognized scientific fact.
Personally, I accepted the facts of evolution long, long before I ever read TGSOE: TEFE (before I ever read any of Dawkins’ books, actually). It was thanks to a good university education that I was able to leave behind my creationist upbringing. So I’m not really one of the people who need to read this book. In many ways, Dawkins is “preaching to the choir”, with me. But I found it an immensely rewarding read, if for no other reason that that it introduced me to lines of evolutionary evidences that even I as a science fan and avid reader of pop-level science literature, had not known about. So this book is doubly valuable: for creationists and other denialists (“history-deniers”, Dawkins calls them), it could very well serve as the intellectual shock that will shake them from those misguided faith systems; and for those who are already well educated about biology and origins, it will reinforce their confidence in science and equip them to better counter creationist nonsense.
Having said that, though, I must admit that I don’t always agree with Dawkins. (On matters unrelated to evolution, I find his anti-religious worldview to be needlessly extreme, overly simplistic, and not a little arrogant.) I think he assumes too much, on occasion. For example, when discussing the longitudinal trend of the tusks of certain African elephants to grow shorter over several decades in the mid-20th century (purportedly, because of the selective pressure exerted by ivory hunters seeking the largest tusks possible), Dawkins seems to utterly disregard the distinct possibility that the data showing the reduction in average tusk size is due not to evolution through selection, but simply to a year-to-year increase in the number of large-tusked elephants being harvested, legally and otherwise. I also think that Dawkins displays a bit of either ignorance or misunderstanding of the philosophy behind certain creationist/Intelligent Design concepts such as “optimal design” and the theodicy behind natural evil.
Richard Dawkins, appearing at the University of Texas, Austin (photo credit: Shane Pope, under Creative Commons 2.0 license)
Still, those are very, very minor issues. (I mention them only to prevent anyone thinking, “You’d believe anything Dawkins says; he’s just your ideological hero.” I find fault in Dawkins’ reasoning and argumentation, as readily as I do, in anyone’s. But since he’s correct about so much in science, the points on which he and I disagree, are rare and small. 
)
Now, a very brief summary of the kinds of evidence Dawkins presents in TGSOE: TEFE. I have not at all included everything that Dawkins presents; I have in fact entirely omitted mention of the more dense discussions of molecular “clocks”, calculations of genetic relationship, and the chapter on evolutionary “arms races” that he includes in the book, but I have noted the basics of the majority of Dawkins’ topics.
Dawkins begins TGSOE: TEFE with a discussion of artificial selection: wolves to dogs, wildflowers to special floral breeds, etc., etc. The creationist criticism here is not at all difficult to imagine: “Artificial selection is just that: artificial. It doesn’t even begin to provide evidence for large-scale evolution.” This may be true (at least, partially) but the reason Dawkins begins with a discussion of artificial selection (and its resultant “micro-evolution”) is twofold. First, it is to prepare the skeptical reader for what is to come, by addressing the types of evolution that very nearly everyone already accepts. Second, as Dawkins points out, artificial selection is essentially just an experiment, which proves natural selection: “Artificial selection constitutes a true experimental–as opposed to observational–test of the hypothesis that selection causes evolutionary change.” (p.66) Dawkins then describes a number of cases that illustrate natural selection, proper (i.e., the evolution of various traits in response to selective pressures, with no human intervention): the co-evolution of flowers and those insects and birds (pollinators) that play a part in their reproduction (p. 80); the lizards of Pod Mrcaru (p.114); John Endler’s studies of the guppies of Venezuela and Trinidad & Tobago (p. 133); etc.
One of the most interesting sections of TGSOE: TEFE is in my view Dawkins’ discussion of transitional fossils. He correctly emphasizes that evolution would stand up well on its own because of other kinds of evidence, even if we entirely lacked fossils. But since creationists make such a big deal about fossils (foolishly and ignorantly, of course, which Dawkins demonstrates), he does address the issue. Since the denialists frequently claim that “there are no intermediate ['missing link'] fossils between species, between genera, etc.,” he offers dozens of examples, although he seems (rightly) to think that he is answering a specious and misguided challenge, to begin with. One of the most interesting ”missing link” fossils is the recently discovered Tiktaalik rosae, a transitional organism somewhere between a fish and an amphibian, which is a demonstable intermediate between Panderichthys and Acanthostega (pp. 167 – 9).* Other examples: Eusthenopteron: a late Devonian fish that had the humerus, radius, and ulna of a tetrapod (p. 166); Ichthyostega, a late-Devonian/early-Carboniferous “salamander-y” fish (p. 167); the aforementioned Acanthostega, which was a similarly amphibian-ish fish, that had lungs and walked on land [!] (p. 167); the ancient dugong Pezosiren, which had legs, unlike its modern, fully-aquatic descendant (p. 173); the ancient ancestor of seals and sea lions, Puijila darwini (p. 172); an ancient forbear of turtles and tortoises, which had only a shell on the abdomen, but not on the back (“turtle on the half-shell” LOL!): Odontochelys semitestacea (p. 174); and the wide range of chronologically well-ordered intermediates that illustrate the evolutionary history of whales: Pakicetus, Ambulocetus, Dalanistes, Rodhocetus, Takracetus, Gaviocetus, Basilosaurus, and Dorudon (p. 171).** Dawkins also (of course) includes a discussion of all the many hominid (i.e., human ancestor) transitional skulls and fossils that have been found.***
[ Perhaps the most famous example of a transitional/intermediate "missing link" fossil is the "part-dinosaur, part-bird" animal whose remains were found in China, Archaeopteryx. Having claws and teeth like a dinosaur, but also feathers and wings like a modern bird, Archaeopteryx seems like an evolutionist's evidence dream. But Dawkins point out that it is a very poor example to cite as a transitional form, because "birds" and "dinosaurs" are so far apart, cladistically speaking, that it is wrong to think that the latter "evolved into" the former. That is, Archaeopteryx is fine evidence for evolution, but not of the idea that dinosaurs became birds. ]
Dawkins also discusses species that appear only on various specific ”islands” (he uses the term loosely, to describe simple geographically isolated environments, that bring about strictly local evolutionary changes). He correctly argues that if evolution were true, we would expect to find areas of the earth in which species have developed in isolation from other species and their gene pools, giving rise to very diverse species on various “islands”. This is in fact exactly what we observe, of course. Dawkins cites the marine iguanas of the Galápagos (p. 261), the many marsupials and eucalyptus trees of Australia (p. 268), the lemurs of Madagascar, the penguins of Antarctica, Platyrrhine mokeys, and certain South American rodents like the capybara, nutria, etc. (p. 269) as creatues that a creator would have had to have decided, rather inscrutably, to “exile” to remote areas of the globe. “Island” species don’t make much sense in a creationist paradigm, but they are perfectly predictable according to evolution, and are better compatible with the latter.
Dawkins devotes a chapter to another set of phenomena that, while not necessarily proving evolution, really only makes sense within an evolutionary history of life on our planet: the presence of skeletal vestiges and homologues. All mammals, for example (and indeed, in a different way, all crustaceans), share the same skeletal body plan; only the proportions of individual respective bones are different: bats, horses, humans, whales, etc., all share the same number of skull bones, “hand” bones, etc., etc. (pp. 288 – 96). This suggests simple historical variation on a basic “body plan” inherited from a common ancestor. Further, the presence of vestigial organs and skeletal formations prove common ancestry and cousinship between species. The human coccyx, for example, is identical in basic structure to the bones that form the base of the tail in mammals that still have a tail (p. 290). Horses, who have only one digit on their hands and feet, retain in their forelegs the bones of those disappeared other “finger” and “toes”; these are called “splint” bones (p. 291).
TGSOE: TEFE contains a long discussion on molecular genetics, and Dawkins cites some lines of evolutionary evidences here that were for me a bit dense, to be honest. However, one study that was conducted did stand out as a great proof of evolution. In 1982, a researcher by the name of Penny compared a specific set of genes among species including humans, kangaroos, dogs, sheep, cows, and chimps. I don’t recall the technical details, but the upshot of the study is this: Upon comparing the variations of the genes in question through a computer program that draws inferences based upon the mathematical rules of probability, it was found that the predicted genetic relationship between any one of these species with another, was exactly as was anticipated according to an evolutionary schema (pp. 323 – 5). In other words, it was found, quantitatively, on a gentic molecular level, that humans are closer cousins to chimps than to cows, and dogs are sheep are closer cousins to cows than they are to us, etc., etc. If evolution were not true, none of these relationships would have been demonstrable on a molecular level.
I probably have done little justice here to Dawkins’ The Greatest Show on Earth: The Evidence for Evolution. But I thought it would be worthwhile to offer my comments on (and praises of) the work. And even though I’ve described here only a small portion of the book’s evolutionary evidences, perhaps it will be enough to encourage others to read the book.
*Interestingly, Tiktaalik rosae played a significant role in the recent court case over Intelligent Design in public school science classes, Kitzmiller et al vs. Dover School Board. Expert witnesses for the plaintiffs (among them the great evolutionary biologist Kenneth Miller) mentioned T. rosae as a specific example of a transitional form, which creationists say don’t exist. The Dover case was, as hardly need be mentioned, decided in favor of science and secular education. T. rosae was not by any stretch the plaintiffs’ only piece of evidence, of course, but it is a great example to cite!
**As if these weren’t enough to show a clear evolution of whales, another transitional whale fossil has just been found, very recently (this month, Feb 2010!). Called Maiacetus inuus, and dating to at least 5 million years ago (IIRC).
***The immensely significant and groundbreaking discovery late last year of Ardipithecus ramidus came too late, apparently, for Dawkins to include in this book. The skeleton of A. ramidus that was found, was palaeolithically dated (using a chemical radioactive “clock” of the surrounding rock layers) to about 4.3 million years ago. The fossil is a transitional between the more ancient hominid ancestors, and those hominids that walked upright and date to no more than 2 million years ago, such as those in the genus Australopithecus (e.g., A. afarensis), and the many transitional fossils in our own genus, Homo (e.g., H. erectus, H. ergaster, H. habilis, etc.).
