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A Brain for All Seasons

Human Evolution and Abrupt Climate Change

One of the most shocking realizations of all time has slowly been dawning on us: the earth’s climate does great flip-flops every few thousand years, and with breathtaking speed. In just a few years, the climate suddenly cools worldwide. With only half the rainfall, severe dust storms whirl across vast areas. Lightning strikes ignite giant forest fires. For most mammals, including our ancestors, populations crash.

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 marvelous 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. Beginning at Darwin’s home in England, Calvin sits under an oak tree and muses on what controls the speed of evolutionary "progress." The Kalahari desert and the Sterkfontein caves in South Africa serve as the backdrop for a discussion of our ancestors’ changing diets. A drought-shrunken lake in Kenya shows how grassy mudflats become great magnets for grazing animals. And in Copenhagen, we learn what ice cores have told us about abrupt jumps in past climates.

Perhaps the most dramatic discovery of all, though, awaits us as we fly with Calvin over the Gulf Stream and Greenland: global warming caused by human-made pollution could paradoxically trigger another sudden episode of global cooling. Because of the accumulation of greenhouse gases in the atmosphere, the oceanic "conveyor belt" 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. Europe would become as cold and dry as Siberia. Agriculture could not adapt quickly enough to avoid worldwide famines and wars over the dwindling food supplies—a crash from which it would take us many centuries to recover.

With this warning, Calvin connects us directly to evolution and the surprises it holds. Highly illustrated, conversational, and learned, A Brain for All Seasons is a fascinating view of where we came from, and where we’re going.

Read an excerpt.

352 pages | 46 halftones, 20 line drawings | 5-1/2 x 8-1/2 | © 2002, 2003

Anthropology: Physical Anthropology

Biological Sciences: Evolutionary Biology, Paleobiology, Geology, and Paleontology

Earth Sciences: Paleontology

Table of Contents

51°N 0°E Darwins home—Catastrophic gradualism
51°N 0°W Evolution House, Kew Gardens—The Darwinian Quality Bootstrap
51°N 1°E Down among the fossils—All of those chimp-human differences
49°N 2°E Musée de lHomme in Paris—The Ghost of Habitats Past
50°N 8°E Bockenheim—Tracing roots back to the Big Bang
52°N 5°E Layover Limbo—IQ and evolutions package deals
22°N 14°E Contemplating the Sahara—Why climate can suddenly flip
0°N 22°E Latitude Zero—Population fluctuations and refugia
19°S 23°E Okavango Delta—The island advantage
25°S 16°E Sossusvlei Dunes—Hominid opportunities in deserts?
26°S 28°E Sterkfontein Caves—The big change in hominid diet
34°S 18°E Cape of Good Hope—The turning point that wasn’t
1°S 37°E Nairobi—Creating new species from old ones
2°S 36°E Olorgesailie—The easiest tool of all
0°S 36°E Kariandusi—A layer cake of handaxes
0°S 36°E Lake Nakuru—Where droughts cause a boom time
1°N 36°E Lake Baringo—The earliest hominids
1°S 36°E Lake Naivasha—Droughts even in good times
3°S 35°E Olduvai Gorge—Degrees of separation
1°S 35°E Maasai Mara—The Crash-Boom-Boom cycle
20°N 15°E Libya by moonlight—The last big step toward humans
52°N 5°E Layover Limbo (again)—The Little Ice Age and its witch hunts
56°N 13°E Copenhagens ice cores—Slow ice ages and abrupt whiplashes
56°N 13°E The plane where its always noon—How ice age climate got the shakes
60°N 11°E High above Oslo—The ocean has a conveyor belt
63°N 6°E Out over the sinking Gulf Stream—Dans coffee cream trick
71°N 8°W Jan Mayen Island—Flushing the Gulf Stream
72°N 12°W The Greenland Sea—Losing the first Panama Canal
74°N 19°W Greenland fjords—What stops the conveyor
75°N 40°W Atop Greenland—Why melting can cause cooling
78°N 69°W Thule—Rube Goldberg cause-and-effect
73°N 95°W Somerset Island—North Poles arent what they used to be
68°N 105°W Crossing the North American coast—How we might stabilize climate
62°N 114°W Yellowknife, Northwest Territories—Feedbacks in the greenhouse
49°N 123°W Bumpy border crossing—Managing high-risk situations
Recommended Reading
Chapter Notes
Subject Index


Phi Beta Kappa: Phi Beta Kappa Award in Science

Foundation for the Future: Walter P. Kistler Book Award

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