From Genesis to Genetics: The Case of Evolution and Creationism

4. Making the Case for Evolution

F O U R Making the Case for Evolution Imagine yourself living in the two decades after the publication of the Origin. You have read Darwin's book as well as reviews, heard several lectures on the subject, and possibly even attended the Oxford debate between Wilberforce and Huxley. If you were not a scientistand were unfamiliar with the workings of scientific procedures, you might be somewhat puzzled and feel unsatisfied with the data availableto Darwin and other naturalists that were regarded as "proofs" of evolution. You might have thought that evolution meant the conversion of one species into another, as the title of Darwin's book suggested; yet not a single example of this conversion was provided in the Origin. Instead, the proofs of evolution consisted of a heterogeneous collection of data: the finding that fossils and living species of armadillos of Argentina are very similar; the restriction of related species in the Galapagos to their own islands; the recapitulation of reptilian jaws in mammalian development; the different kidneys in embryos and adults of vertebrates ; vestigial organs such as the human appendix. Would you have found the Origin convincing? The proofs of evolution do not come from the experimental demonstration of one species changing into another. Such direct evidence will always be absent except for unusual situations because the change 92 / Making the Casefor Evolution of one species into another may take many thousands of years-and none of us is able to wait that long for definitive proof. Instead, we have to put together bits of evidence that, with luck, will provide a plausible explanation of what occurred. A detective may study the grooves on the murder bullet, trace the activities of suspects, wonder why the household dog did not bark, compare the DNA in a drop of blood at the murder scene with that of suspects, and seek a motive. Neither the detective not the evolutionist observes the events that require explanation. Both, however, proceed in a similar manner and reach a highly likely conclusion. The data that prompt biologists and paleontologists to accept evolution as the most accurate statement possible about the diversity of life are indirect, but each piece is consistent with the concept of evolution . Although we cannot "see" evolution on any major scale, much of the data of biology and paleontology cannot be understood without it. Furthermore, the theory of evolution continues to suggest new ways of obtaining further understanding of the origin and diversificationof life over the ages. There is no other scientific theory that has proven to be as useful, and for this reason evolution is now accepted as true beyond all reasonable doubt. Evidence for most of the data that convince scientists is rarely convincing , or even understood, by nonscientists. For example, most people accept what astronomers tell us-that the rotation of the Earth on its axis is the cause of night and day-but can laypeople recite the evidence that this is so? Not likely. To take a more recent example, a layperson who is shown the data on the temperatures in deep space and the change in the spectral lines of light from distant galaxies probably cannot figure out that these data are evidence for the Big Bang that started the universe 12-15 billion years ago. If a nonspecialist accepts the Big Bang as a useful concept, it is because he or she has confidence that astrophysicistsare giving the best explanation they can on the basis of available evidence. There is no strict way scientists-or detectives-go about their Making the Casefor Evolution / 93 quests for answers. There is no one rigid scientific method, but scientists do follow in a general way a series of steps. First, they formulate a question about some natural phenomenon that needs to be explained. The one evolutionists start with is: How can we provide a scientific explanation for the many kinds of organisms that lived in the past and are alive today? The next step is to guess what an answer might be. That guess, or hypothesis, is almost always based on preliminary observations from nature or data from experiments that make the hypothesis plausible. In Darwin's case, he based his hypothesis on his observations of geographic variation among animals and plants in the Galapagos and on the resemblance of fossils in Argentina to living species found there. Both observations could be explained by the hypothesis...