In 1859 Darwin described a deceptively simple mechanism that he called "natural selection," a combination of variation, inheritance, and reproductive success. He argued that this mechanism was the key to explaining the most puzzling features of the natural world, and science and philosophy were changed forever as a result. The exact nature of the Darwinian process has been controversial ever since, however. Godfrey-Smith draws on new developments in biology, philosophy of science, and other fields to give a new analysis and extension of Darwin's idea. The central concept used is that of a...