Can Whiplash Climate Changes Explain the Ape-to-Man Jump?
New evidence points to radical shifts in the weather as the surprising catalyst for human evolution By Corey S. Powell A Brain for All Seasons: Human Evolution & Abrupt Climate Change By William H. Calvin University of Chicago Press, $25 We frequently get letters at Discover from skeptics who question the notion that humans have descended from apes. And we have to admit that even dedicated Darwinians are baffled by a conundrum of evolution: How did humans diverge so sharply and rapidly from other primates and emerge as large-brained, chatty, and sociable? William Calvin, a behavioral scientist at the University of Washington, offers a surprising answer in A Brain for All Seasons: Blame the weather. The basic theory of natural selection suggests that evolutionary change grows out of the random variations found in any population. Depending on local conditions, some organisms will be more successful than others: They might have slightly thinner fur, smaller teeth, or some other traits tha