Is natural selection the best explanation of evolution?
Natural selection is often described as the best explanation of how evolution happened, and numerous examples demonstrate that it is an important force controlling evolution. Polar bears offer one example. They hunt in the snowy arctic; they sneak up on their prey; and they are, after all, white. Thus they appear to be well adapted to their environment. Many features in the history of life, however, suggest that chance has played a very important role in evolution, too. For example, several times in the history of life, mass extinctions have occurred–events so severe that they eliminated most of the species on Earth. Such a mass extinction ended the dinosaurs’ reign at the end of the Cretaceous Period. Prior to the mass extinction, dinosaurs were large and dominated the world, whereas mammals were small and nocturnal, sneaking around in the dinosaurs’ world. It was not until the dinosaurs went extinct that the mammals could take over and flourish. The mechanism that caused this extinc
