First the bad news. "One of the most shocking scientific realizations of all time has slowly been dawning on us," William Calvin announces in the opening words of his new book: "the earth's climate does great flip-flops every few thousand years, and with breathtaking speed." For the last 8,000 years or so, we've enjoyed an unusually stable climate. But there's no reason to suppose that it will continue indefinitely—in fact, if geological history is any guide, we can be pretty sure it won't. Imagine the disruptions associated with the Little Ice Age (a.d. 1300-1850) but on a much larger scale and concentrated in a single decade. An episode of abrupt global cooling, such as has occurred many times in Earth's history, would create massive food shortages and could easily lead to worldwide conflict—"taking much of civilization with it."

Alarmist? Absurd? Wildly apocalyptic? Calvin isn't predicting such an outcome; rather, he's suggesting that it is a real possibility, worth pondering. He observes that the last episode of abrupt global cooling, the so-called Younger Dryas, "drastically altered Europe's climate as far east as Ukraine." Starting about 15,000 years ago, the Earth had been thawing out from the last major Ice Age. But about 12,900 years ago, "just in a matter of a decade or so, the climate flipped from warm-and-wet into the cool-and-dry mode, with temperatures plunging back to what they had been in the ice ages."

Today, Europe's population of more than 650 million is fed mostly by food grown in Europe. With a climate change like the Younger Dryas, Europe might be able to support a population comparable to Canada's. Lacking present-day Europe's "winter warmth and rainfall," Calvin notes, Canada is able to support a population of only 28 million despite its huge expanse.

The good news is that we recognize the problem, and we may even be able to do something about it. "Until a dozen years ago," Calvin writes, "everyone lived in blissful ignorance about the severe climate flips that happen quickly, with just a few short years before hard times set in with a vengeance." Now there's growing awareness that the old model of very gradual climate change is defective.

Calvin was one of the first scientists to bring this new consensus to the attention of the general reader; his January 1998 Atlantic Monthly cover story, "The Great Climate Flip-Flop," provoked an enormous response (including howls of indignation and disdain from those who saw his article as the latest exercise in environmental scare-mongering). More recently, readers of Books & Culture may recall Catherine Crouch's review of Richard Alley's book, The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future. And Elizabeth Kolbert's New Yorker article, "Ice Memory: Does a glacier hold the secret of how civilization began—and how it may end?", covers some of the same territory.1 Maybe the people who made the animated feature, Ice Age, have been reading this stuff, too.

One of the purposes of Calvin's new book, A Brain for All Seasons: Human Evolution and Abrupt Climate Change, is to build on that Atlantic Monthly article, taking into account criticisms against it and knowledge gained in the interim. Much of the criticism of Calvin's article centered on the global warming debate. Yes, Calvin—like Richard Alley and many others—believes that human-caused global warming increases the likelihood of an abrupt "flip" to global cooling. Readers who saw the sequence of photographs on the front page of The New York Times for March 20 ("Large Ice Shelf in Antarctica Disintegrates at Great Speed") had good cause to feel uneasy.

But even if we bracket out the question of human impact and global warming (a subject that arouses irrational passions, though the scientific consensus is clear), we're left with a record of rapid climate changes occurring again and again—and the high probability that more of the same can be expected. Hence Calvin's call for a massive effort (not least through computer modeling) to assess the situation and develop strategies that might mitigate an abrupt climate shift seems simply prudent.

At the same time, as the title of Calvin's book makes clear, he's not only interested in climate. By training he's a neurobiologist, not a geoscientist; currently he is an affiliate professor of psychiatry and behavioral sciences at the University of Washington School of Medicine. By disposition he's insatiably curious, and he has a rare gift to pull together learning from diverse fields for a big-picture view. You can see that in his books: How Brains Think, The River That Flows Uphill, Conversations with Neil's Brain, and many more.

In A Brain for All Seasons, he takes on a question that's animated dozens of books lately: How did we—humans, that is, or "behaviorally modern humans," as Calvin says—get this way? Why are we so different not only from chimps and other primates but also from other hominids, including earlier versions of Homo sapiens? What drove the development of "higher intellectual functions" that appeared rather suddenly 50,000 years ago (or further back, some are now saying)?

Quite a range of answers are on offer. One of my favorites is the meat-eating theory, as expounded in books such as Craig Stanford's The Hunting Apes: Meat Eating and the Origins of Human Behavior. Oh, that explains it! (I see in my mind's eye Victor Mature in One Million B.C.: is that a mastodon drumstick he's gnawing on?) Michael Corballis weighed in with The Lopsided Ape: Evolution of the Generative Mind, starting from the observation that humans are the only primates that are predominantly right-handed. And so on.

Calvin's not a monocausal guy, but he puts heavy weight on the demands of abrupt climate change: rapid cooling, less rainfall, high winds, dust storms, fires. Animal populations decimated. "Our ancestors," Calvin writes, "lived through hundreds of such episodes—but each became a population bottleneck, one that eliminated most of their relatives. We are the improbable descendants of those who survived—and later thrived." This, more than any other factor, he suggests, shaped the development of our highly versatile "brain for all seasons" and the full "modern suite of mental abilities."

The book is structured as a "Human Evolution E-Seminar," with Calvin sending bulletins from places all over the globe pertinent to his story. (And he includes his own email address on the title page, as well as a link to a website for the book: there's a generosity to this project, a sharing of information and openness to exchange, characteristic of science at its best.) Thus, whether or not one finds his emphasis on climate persuasive, these pages have a wealth of observation and insight to offer. (And some of the foolishness endemic to the genre, including hyperbolic paeans to Darwin and asides like this: "A window seat in the stratosphere certainly provides a better place from which to contemplate the world than most philosophers ever had." Those poor benighted philosophers!)

For Christian readers, Calvin's book is also a reminder of ongoing questions. David Livingstone has shown that Christians have been wrestling with the significance of preadamic hominids for much longer than we may suppose; still, never has the need been more urgent for a theological anthropology that acknowledges the biblical revelation of the unique nature of humans as created in the image of God while taking full account of all we are learning about the history of life. For Christians, the ultimate answer to the question How did we get this way? is clear: God created humans thus. But that leaves much of lesser but not trivial significance unsettled.2

Apart from such all-too-familiar conundrums, Calvin's tale of sudden and disastrous climate change challenges our assumptions about the order of things and reminds us of the greater mysteries of providence. All of recorded history has taken place in what Calvin calls "an unprecedented period of climate stability." He adds:

Why the relative stability for eight millennia? No one knows, yet. But we know that it is unusual, and see no reason why it should persist.

This much we do know: the God who spoke to Job from the whirlwind exceeds our understanding, and always will, and yet he cares for us. And he has created us to be good stewards of his creation—a job description William Calvin would heartily endorse.

1. Catherine H. Crouch, "Reading the Ice Cores," Books & Culture, July/August 2001, p. 6; Elizabeth Kolbert, "Ice Memory," The New Yorker, January 7, 2002, p. 30.

2. David N. Livingstone, The Preadamite Theory and the Marriage of Science and Religion, Transactions of the American Philosophical Society, Vol. 82, Part 3 (1992). See also Davis A. Young, "The Antiquity and the Unity of the Human Race Revisited," Christian Scholar's Review, Vol. 24, No. 4 (1995), pp. 380-396.

Copyright © 2002 by the author or Christianity Today/Books & Culture magazine.
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