Scientific American (July 2002) REVIEWS
June 17, 2002
Climatic and Evolutionary Whiplash
How sudden shifts in climate may have boosted human ingenuity

A Brain for All Seasons: Human Evolution and Abrupt Climate Change
by William H. Calvin
University of Chicago Press, 2002
Imagine going to the first meeting of a course you'd long waited to enroll in. You sit down at your computer, open an e-mail message from your professor, in this case the author William H. Calvin, and get your first lesson. Your professor is thousands of miles away. In fact, he's at 51.4N, 0.1E. Where? Why, Charles Darwin's home in Kent, England, of course, the famous Down House.

So begins Calvin's journey through evolution, particularly human evolution, as he leads his "class" from the home of the man many would call the father of evolution to various locales that provide fodder for his ultimate message: human evolution, like that of other organisms, is not a gradual transformation of form and behavior over time. Rather, like the shifts in the environments in which organisms find themselves, evolutionary change is abrupt, even catastrophic. A neurobiologist by training (he is at the University of Washington School of Medicine), Calvin leads us along a trail that links sudden worldwide coolings to the origin of our large brains and modern human behavior. By modern behavior, he is thinking not just of sophisticated toolmaking; he includes such social behavior as pair bonding and, ultimately, language, a sense of the aesthetic, and "abstract thinking, planning depth, innovation, and symbolic behavior."

The sudden coolings, Calvin tells us, reduced rainfall, induced dust storms and fires, and produced bottlenecks in the populations of our forebears. The few survivors had to adapt within one generation to, for example, a climate in which only grass grew well, spurring them to develop innovative techniques for hunting the large grazing animals that converted the grass into edible energy. Thus, he concludes, the cycles of "cool, crash, and burn" drove increased brain size and complexity. I think it unlikely that the climatic shifts were behind changes in the physical size and complexity of the brain, but these sudden jolts could certainly have spurred early humans to exploit the existing potential of the brain.

To make his points, Calvin takes us,
Fossilized cast of early hominid brain (Australopithecus africanus), about 2.5 million years old.

FOSSILIZED CAST of early hominid brain (Australopithecus africanus), about 2.5 million years old.
his class, on a peripatetic journey as he visits museums, attends conferences, pays homage to a variety of African human fossil sites, and flies over huge African expanses and the vast Nordic seas. As one might expect, this approach is not always successful, but if you forget the formatting at the beginning of each brief chapter (a nod toward an e-mail message, but one without typos, code abbreviations and non sequiturs), the read flows a bit better.

Calvin's premise--that human evolution is correlated with climatic swings--is, of course, not new. Indeed, the traditional Darwinian view holds that evolution proceeds through organisms tracking their environments. And well over a decade ago paleontologist Elisabeth Vrba proposed that changes in species representation over time, as evidenced especially in the South African fossil record of antelopes and early hominids (such as Australopithecus and Paranthropus), were rapid and correlated with shifts between wetter and drier conditions.

But Calvin's presentation differs from the others in that it really is an attempt to think globally about past and present climatic change and its possible effects on creatures and their evolution. As one of the authors whose work on human evolution he cites as recommended reading, I found his discussion of the fossils less engaging than the climate-related information. The book definitely picks up steam when he moves away from trying to discuss human fossils and digs into issues of global warming, shrinking polar ice caps, and oceanic currents. (This may be because much of this section had already been published as "The Great Climate Flip-Flop" in the Atlantic Monthly.) Here he seems to have more fun, getting across an image, for example, of subsurface oceanic water behavior by describing what happens when you pour very cold heavy cream over a spoon into a cup of hot coffee (it sinks as a column) and explaining North Atlantic Ocean current movements by way of a story about incorrectly hooking up a hot-water tank with a toilet that then acted as a radiator.

Heading back home to Seattle on the long, great-circle-route flight from Nairobi, over the Gulf Stream and Greenland, Calvin muses on the present global warming brought about by human activities. It could, he says, paradoxically trigger another episode of sudden cooling. The accumulation of greenhouse gases in the atmosphere could induce an abrupt shutting down of the oceanic "conveyor belt" that sends warmer waters into the North Atlantic, plunging much of the earth into a deep chill. But he doubts that another boom-then-bust cycle will jack up our brain power. We're now smart, he concludes, "in ways that owe little to our present brain power, but rather to the accumulated experience of the people that have lived since the last ice age ended. Education. Writing. Technology. Science." And he suggests that if we're really smart, our accumulated experience may just help us find a way to avoid this looming threat.

The Author(s):

Jeffrey H. Schwartz teaches physical anthropology at the University of Pittsburgh and is author of Sudden Origins: Fossils, Genes and the Origin of Species (Wiley, 1999).

from The Guardian (April 14, 2002)

How Ice Ages increased our brainpower

Extreme climate change has been linked to humanity's giant mental leap forward

Robin McKie

Sunday April 14, 2002


Scientists believe climate catastrophes that triggered droughts and forest fires in mankind's African homeland two million years ago were responsible for the evolution of our large brains.

Faced with massive, rapid changes to their woodland homes, early humans had rapidly to learn to live in a changing landscape. Only those with the most flexible, adaptive minds survived.

'Climate change is the engine of evolutionary change, and it drove the development of our brains,' said US brain expert William Calvin, of the University of Washington School of Medicine.

Scientists have long known that mankind began using stone tools 2.5 million years ago and that around this time the world entered a period of considerable climatic instability. Ice ages brought major weather changes to all parts of the globe.

However, researchers had thought that these changes took decades or even centuries to take effect. 'It has only recently become apparent that climate change would have struck very quickly, producing major changes in one or two years,' said Calvin, who outlines his theory in Brain for All Seasons (Chicago University Press), which is published this week.

Although Africa - home of our Homo erectus ancestors - would have been protected against the worst effects of global cooling, it would have suffered severe droughts. Vast tracts of forest would have dried to tinder within a couple of years to be destroyed by fires sweeping the woodlands. Over succeeding decades, the environment would have recovered, only for the process to be repeated a century or two later.

With the destruction of our ancestors' woodland homes, most of their food sources would have been swept away, leaving them with little to eat except grass and large animals, such as antelopes. They would have had little alternative than to hunt these creatures, in the process creating a problem: each big kill would have produced far too much meat for each group of hunters, so they started sharing with others, in the expectation of being given food when someone else succeeded.

Thus the idea of sharing and trust, the linchpins of human society, would have been born as our ancestors tried to survive. 'In effect, we are the children of the Phoenix generation,' said Calvin.

Slowly our brains grew, partly to cope with the pressures of dealing with societies and cultures that were becoming more and more complex, but also to develop the means to adapt to the different ecological niches that were being created at the time, an idea that is also backed by Richard Potts of the Smithsonian Institute in Washington.

'About 2.5 million years ago, hominids encountered great fluctuations in the climate,' he said. 'At the same time, we see the appearance of stone tools. That is no coincidence. They indicate that that at least one species of hominid was responding to these changes by becoming even more adaptable.'

The end result was Homo sapiens, a creature marked by its ability to make tools and instruments - harpoons, guns, spears, and fishing nets - that allow us to exploit all sorts of varying ecological niches, and which give us unprecedented flexibility as a species.

'Essentially, we now carry our environments around with us, in the form of tools and clothes,' said Professor Chris Stringer of the Natural History Museum, in London. 'We had to learn to do that because the environment we evolved in was unpredictable and changeable. Climate made us what we are today.'

Whether humanity can continue to evolve in, or even survive further climatic mayhem, is a different matter, as Calvin acknowledges.

'Were a cold flip to happen in our now crowded world, dependent on agricultural productivity and efficient supply lines, much of civilisation would be ruined in a series of wars over the shrinking food supply,' he said.

· Additional research by Hannah Richards.

Guardian Unlimited © Guardian Newspapers Limited 2002

from Discover (June 2002)


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 that prove beneficial. The average form and features of the next generation will be slightly different because of unequal survival rates, and the cycle repeats. Scientists traditionally pictured this process happening in a leisurely manner, nudged along in part by gradual environmental shifts. Beginning in the mid-1980s, however, a number of researchers recognized that Earth's climate sometimes changes drastically in just a few years. Those crazy times, Calvin argues, are the key to understanding human origins.

During whiplash climate changes, temperatures plunge and horrible droughts set in. Calvin envisions groups of hominids migrating to shriveled lakes and watering holes, drawn by the concentration of game animals. In such relatively compact social settings, altruism might have been a useful strategy for those protohumans able to recall which individuals had shared fairly and which had not. The herds of prey loitering around the watering hole might also have encouraged cooperative, semiskilled hunting by using what Calvin describes as Killer Frisbees—the enigmatic triangular stones with sharpened edges found at many hominid fossil sites. Ecological crises occurred repeatedly over the past two and a half million years, especially during the ice ages of the last 117,000 years. Each swing of the climate weeded out large parts of the population, favoring the large-brained hominid generalists who could survive when water was scarce and then thrive in the lush savanna once the rains returned.

All of this is necessarily speculative. Many behaviors do not leave any traces, and fossils are much more effective at recording what happened rather than why. Calvin addresses these uncertainties and invites readers to examine his evidence by structuring the book as a travelogue. You join him as he watches the animals around a Masai watering hole, observes sea ice floating off Greenland, and accompanies a fossil excavation in the Sterkfontein Grotto of South Africa. The flood of information is persuasive, if a little overwhelming.

Why don't we see great leaps in primate evolution now? One part of the answer is that major changes generally take a long time for slow-reproducing creatures like ourselves. But radical climate changes could quickly do a number on us, Calvin warns: "The result would be a population crash that would take much of civilization with it, all within a decade."

From A Brain for All Seasons, p. 8:
We could go back to ice-age temperatures within a decade—and judging from recent discoveries, an abrupt cooling could be triggered by our current global-warming trend. Europe's climate could become more like Siberia's.



Seattle Times

Entertainment & the Arts: Friday, May 17, 2002

Book Review
UW professor's new book warns of global warming's evil, icy twin

By David Williams
Special to The Seattle Times

E-mail E-mail this article
Print Print this article



Despite what our president, a few scientists, oil-company spokesmen and the Big Three automakers say, global warming is here. This is not a new story. Anyone who has paid attention knows that global warming could have drastic effects.

What most stories fail to report is that many researchers are less concerned by global warming than by its evil twin: immediate and dramatic cooling, which could lead to a catastrophic ice age that could take over the globe.

Such a rapid cooling, although a relatively new news story, is not an unusual event in Earth's history. Abrupt climate change has occurred scores of times in just the past 2.5 million years, a period that corresponds with critical evolutionary events in our ancestors' history. We may understandably fear these shifts, but without them our species might not exist, or so writes William H. Calvin in his newest book, "A Brain for All Seasons."

Author reading

William H. Calvin will read from "A Brain for All Seasons: Human Evolution & Abrupt Climate Change" at 7:30 p.m. Wednesday, Elliott Bay Book Co., 101 S. Main St., Seattle; free, 206-624-6600.

A professor of psychiatry and behavioral sciences at the University of Washington, Calvin focuses his research on the brain, and in particular our species. His previous books include "Lingua ex Machina," "The River That Flows Uphill," and "How Brains Think." "A Brain for All Seasons" grew out of his January 1998 article, "The Great Climate Flip-Flop," in The Atlantic Monthly.

Calvin's basic premise is that climatic flip-flops from warm and wet to cold and dry have happened often, every few thousand years, and appeared quickly, in less than a decade. They have led to widespread fires and extensive drought, exacerbated by severe windstorms. The resulting devastation caused population crashes of many species, including our ancestors. A few survived, however, only to have their descendants go through the process over and over again.

One of the consequences of such whiplash changes in climate and population is that hominid survivors learned to adapt to eating grass, a key post-inferno colonizer. They didn't necessarily actually eat the grass but did consume those who consumed grass, the big grazing animals that survived the droughts, too. This adaptation is the one that Calvin believes led to the rapid increase in hominid brain size over the past 2.5 million years, a development that produced such essential human traits as toolmaking, cooperation and planning.

Changes in the circulation pattern of ocean currents along Greenland drive the flips. These currents carry warm water, rich in excess salt, from the tropics. When the salt reaches the north, it sinks and carries with it cooled surface water, which gets transported back south. If the conveyor belt stopped, then Europe would have a cold and dry climate like Canada, and the planet would settle into an ice age.

Calvin makes a convincing argument for his thesis by tracing his ideas across the globe and writing in what he calls an "E-seminar" style of travel briefs. Roughly half his accounts come from Africa, where he delves most deeply into our evolutionary past. Each seminar is short, fact-filled and conversational. Nearly 40 pages of glossary and footnotes supplement the book.

Calvin also includes numerous Web sites for further reference. In addition, he has posted the entire text of the book on his Web site,, including color photographs of the black-and-white shots included in the text.

Like other books on evolution and/or climate change, Calvin's book addresses the present and future, in addition to the past. He argues that although scientists have evidence for our changing climate, we still need more research. More important, we need it quickly. We can only hope that we can adapt and respond as readily as our predecessors.

Copyright © 2002 The Seattle Times Company