This chapter discusses distinctive features of Darwin’s theory of evolution, noting when they coincide with contemporary biology and when they depart. Darwin held ● that all life on earth today traces back to a common ancestor ● that natural selection is the main but not the exclusive cause of evolution ● that evolution is opportunistic, not pre-programmed ● that natural selection often causes traits to evolve because they help the organisms that have them to survive and reproduce, but sometimes selection causes traits to evolve because they help groups to avoid extinction and to found new daughter groups ● that evolution by natural selection is a gradual process ● that novel traits (now called mutations) have their causes, but they do not happen because they would be good for the organisms in which they occur ● that the distinction between species and sub-specific varieties is a matter of convention ● that middling phenotypes are usually fitter than phenotypes that are more extreme ● that traits acquired in the life-time of parents can be passed along as inherited characteristics to offspring.