"The earth's climate does great flip-flops every few thousand years. Our ancestors lived through hundreds of such abrupt episodes since the more gradual Ice Ages began two and a half million years ago - but abrupt cooling produced a population bottleneck each time, one that eliminated most of their relatives. We are the improbable descendants of those who survived - and later thrived." "William H. Calvin's A Brain for All Seasons argues that such cycles of cool, crash, and burn powered the pump for the enormous increase in brain size and complexity in human beings. Driven by the imperative to adapt within a generation to "whiplash" climate changes where only grass did well for a while, our ancestors learned to cooperate and innovate in hunting large grazing animals." "Calvin's book is structured as a travelogue that takes us around the globe and back in time, up to the present when, because of the accumulation of greenhouse gases in the atmosphere, the ocean current that sends warmer waters into the North Atlantic could abruptly shut down. If that happens again, much of the earth could be plunged into a deep chill within a few years."--BOOK JACKET.