There is a notorious book for creationists titled _Evolution: The Fossils Say No!_ It gets right to its point in its title which accomplishes two things. One is to claim that fossils do not say what overwhelmingly biologists and geologists say they say. The other is to emphasize that fossils are the chief evidence evolution can muster. That might have been true a hundred years ago, but now, even if we had no fossils to study, we would still have wonderfully abundant evidence of evolution happening and just how it happened. We can now look directly at the DNA in animals that have evolved from previous ancestors and see indubitable chains of linkage. Sean B. Carroll, a professor of genetics, relates the stories scientists are coaxing from the molecules of genes in _The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution_ (Norton). He points out in his preface that there is wide public acceptance and understanding of DNA testing in solving crimes; DNA can provide testimony about who was present at a crime scene with far more trustworthiness than fingerprints or eyewitness recollection. Yet polls consistently show that something like half of the public in the United States are more likely to go with the anti-Darwinian ideas in _Evolution: The Fossils Say No!_ than they are to subscribe to the theory of evolution. It is Carroll's aim to have readers consider the DNA evidence for evolution as strong as DNA evidence from crime scenes, and his clear and entertaining book does just that. "Every evolutionary change between species, from physical form to digestive metabolism," he writes, "is due to - and recorded in - DNA. So, too, is the 'paternity' of species. DNA contains, therefore, the ultimate forensic record of evolution." Carroll's book gives plenty of fascinating instances of evidence for that DNA record.
He starts with a fish that has no red blood cells. Before it was found, biologists taught that all vertebrates had red blood cells containing the hemoglobin that carries oxygen, and when there were stories of fish without blood in the Antarctic, they were assumed to be just stories. But in 1954, biologists were amazed to read a report of the icefish, so called because it looks transparent; it has no red blood cells to block the light. There is no fossil record for these fishes, but the DNA is there, although it could only tell the story of the icefish's evolution forty years after their blood was first sampled. The DNA that codes for red blood cells in fish and the rest of us is there, but only partially, and in an eroded form that cannot work. One of the lessons Carroll consistently draws is that in evolution, there is a "use it or lose it" dictum. Genes change, even if mutation rates are low; if the change is deleterious, it might be that the organism is sufficiently wounded that it gets no chance to pass the gene on. It also might be that other genes make up for the change, and if so, the changed gene gets passed to the next generation, but since it does not work, it can further decay as it is passed further down. In this fashion, natural selection maintains working genes, and ignores inoperative ones. The icefish DNA for hemoglobin is eroded, but it is still there from the time of its ancestors that had hemoglobin. (This is a perfect argument against some supernatural designer building the fish in this way: what would be the point of including eroded, nonfunctional DNA?) It does not do anything but get copied, perhaps imperfectly, for succeeding generations; the icefish has made other changes to do without hemoglobin, using a blood that is literally ice water, a large volume of it pumped by a large heart, to take advantage of the high solubility of the oxygen in icy waters. Carroll gives plenty of other fascinating examples of tracking evolution in this way.
Carroll gives an excellent but simple explanation of the mathematics of evolution, showing that while most mutations are, as the creationists remind us, harmful, that does not preclude a tiny fraction from being helpful, and the odds of this tiny fraction occurring in large populations over millions of years is quite formidable. In discussing why people may rely on irrational or non-scientific explanations, he turns to the example of Trofim Lysenko, whose unscientific and yet state-sponsored ideas of inheritance nullified for years any biological advancement within the Soviet Union. He also finds that the tactics of chiropractors in opposition to vaccination (such as exaggerating disagreements between scientists) are the same as creationists use in opposition to evolution. Science works, and it does not become iffy just because it turns its attention to a branch of nature that has implications against literal interpretation of scriptures. Carroll makes plain that such a religious expert as Pope John Paul II accepted evolution as science (although there has been some Catholic backlash in the past year); clearly there are some Christians who do not see evolution as a threat. In a final chapter, he makes clear that this is not just a matter of whether or not we teach evolution in the schools, for looking at problems like overfishing or the biological effects of global warming can only be understood in evolutionary terms, unimpeded by religious or governmental authority. It may be too much to ask that those who get their biology and history from religious authorities will read Carroll and understand how overwhelming (and beautiful) is the new evidence for evolution, but he has given an excellent summary for all to try.
