Why Evolution Is True by Jerry A. Coyne Read Free Book Online

makes predictions that are bold and clear. Darwin spent some twenty years amassing evidence for his theory before publishing The Origin. That was more than a hundred and fifty years ago. So much knowledge has accumulated since then! So many more fossils found; so many more species collected and their distributions mapped around the world; so much more work in uncovering the evolutionary relationships of different species. And whole new branches of science, undreamt of by Darwin, have arisen, including molecular biology and systematics, the study of how organisms are related.
    As we’ll see, all the evidence—both old and new—leads ineluctably to the conclusion that evolution is true.

Chapter 2
    Written in the Rocks
    The crust of the earth is a vast museum; but the natural collections have been made only at intervals of time immensely remote.
     
— Charles Darwin, On the Origin of Species
     
     
     
    T he story of life on earth is written in the rocks. True, this is a history book torn and twisted, with remnants of pages scattered about, but it is there, and significant portions are still legible. Paleontologists have worked tirelessly to piece together the tangible historical evidence for evolution: the fossil record.
    When we admire breathtalting fossils such as the great dinosaur skeletons that grace our natural history museums, it is easy to forget just how much effort has gone into discovering, extracting, preparing, and describing them. Time-consuming, expensive, and risky expeditions to remote and inhospitable corners of the world are often involved. My University of Chicago colleague Paul Sereno, for instance, studies African dinosaurs, and many of the most interesting fossils lie smack in the middle of the Sahara Desert. He and his colleagues have braved political troubles, bandits, disease, and of course the rigors of the desert itself to discover remarkable new species such as Afrovenator abakensis and jobaria tiguidensis, specimens that have helped rewrite the story of dinosaur evolution.
    Such discoveries involve true dedication to science, many years of painstaking work, persistence, and courage—as well as a healthy dose of luck. But many paleontologists would risk their lives for finds like these. To biologists, fossils are as valuable as gold dust. Without them, we’d have only a sketchy outline of evolution. All we could do would be to study living species and try to infer evolutionary relationships through similarities in form, development, and DNA sequence. We would know, for example, that mammals are more closely related to reptiles than to amphibians. But we wouldn’t know what their common ancestors looked like. We’d have no inkling of giant dinosaurs, some as large as trucks, or of our early australopithecine ancestors, small-brained but walking erect. Much of what we’d like to know about evolution would remain a mystery. Fortunately, advances in physics, geology, and biochemistry, along with the daring and persistence of scientists throughout the world, have provided these precious insights into the past.

Making the Record
    FOSSILS HAVE BEEN KNOWN since ancient times: Aristotle discussed them, and fossils of the beaked dinosaur Protoceratops may have given rise to the mythological griffin of the ancient Greeks. But the real meaning of fossils wasn’t appreciated until much later. Even in the nineteenth century, they were simply explained away as products of supernatural forces, organisms buried in Noah’s flood, or remains of still-living species inhabiting remote and uncharted parts of the globe.
    But within these petrified remains lies the history of life. How can we decipher that history? First, of course, you need the fossils—lots of them. Then you have to put them in the proper order, from oldest to youngest. And then you must find out exactly when they were formed. Each of these requirements comes with its own set of challenges.
    The formation of fossils is straightforward, but