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Last Updated on May 6, 2015, by eNotes Editorial. Word Count: 1902

This fascinating work is sprinkled with tidbits from archaeology and seasoned with quotations from sources as varied as novelist Mark Twain and physicist Werner Heisenberg. While William H. Calvin’s stated agenda is to explain his theory that abrupt climate change influenced the development of the human brain, he focuses much more on explaining the mechanisms that effect climate change in the past and in the present. This is a bit of a disappointment, as a book with such a tantalizing premise, which actually does provide strong factual support for his ideas and brings the discussion within reach of most interested readers, abandons the issue of brain development altogether in its final chapters. The final fourteen chapters of the book, nearly one third of the text, are concerned almost exclusively with explaining abrupt climate change, its possible effects, and what can be done to prevent it. The book jacket reveals that this final third of the book is based on an article he wrote for The Atlantic Monthly entitled “The Great Climate Flip-Flop.”

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The book is divided into thirty-five chapters, and each chapter heading is presented as an e-mail addressed to the “Human Evolution E-Seminar” from Calvin. The chapters also follow an overflight of the globe, and Calvin gives his location in degrees longitude and latitude. In his “Afterthoughts” section, however, Calvin admits that he has never actually given any e-seminars, let alone this one, and that “the present framework is an amalgamation of various European and African trips, meetings, and over-the-pole flights between 1999 and 2001, rearranged to suit thematic development.” Whether or not he decided on the e-seminar as an attractive gimmick for modern audiences, it does not intrude much on the reading experience and can be ignored rather easily. Calvin’s style is smooth, chatty, and filled with anecdotes. Any reader who is interested in this subject will find his ideas and the way he brings the reader to them easy to comprehend but hardly simple-minded. Calvin is serious about his subject and seeks information from experts in the fields of paleoarchaeology and climatology, which he amply shares with the reader. His sincerity comes through especially in his explanations of the climate phenomena that humans depend upon and his pleas to pay attention while it may still be possible to do something to stabilize the current favorable climate.

In his “Preamble,” Calvin sets out his basic theory. The existence of the ice ages of the past has long been known; however, it has only recently been discovered that the planet’s climate has experienced not only gradual changes, but also sudden and drastic “flip-flops” every few thousand years. The examination of ice cores and cores from ocean floors and undisturbed ancient lake beds reveal these worldwide climate changes. The current warm period, during which humankind invented agriculture and built civilizations dependent on its success, has lasted for an unprecedented length of time. Why this uninterrupted good time exists is unknown. Human ancestors were subject to climate changes that caused populations to crash and ecosystems to collapse. Within a single generation, the old ways of sustaining life disappeared and only those who were able to take advantage of the new situations that the climate change brought survived to continue the species.

The first chapter begins the “journey” of this book at Charles Darwin’s country home in Downe, England. Calvin states that most people do not understand the principles of evolution that Darwin wrote about and enumerates five important elements that speed up evolution: speciation; sex (or mating); populations separated into islands; “empty niches” in which competition is absent; and climate fluctuations. Like a committee, Calvin says, these five elements work together to force change.

The second chapter takes Calvin to France and to an examination of the fossil record. Fossil evidence shows that there was not a single hominid species that led directly from apelike ancestors to Homo sapiens, or modern humans. Instead, several different species arose, just as the gorillas, orangutans, and chimpanzees are different branches arising from that more distant ancestor. Once it was thought that Neanderthals were part of the human line, but now it appears that both it and Homo erectus were different evolutionary experiments that died out, leaving the ancestors of Homo sapiens as the only hominid species to continue to the present day. While researchers are limited in their ability to determine exactly how and why hominid populations crashed, climate change and its effects on local ecologies were crucial.

The ice ages are generally discussed as though their colder temperatures were their most important factor, but Calvin writes that temperatures worldwide during the ice ages were really only a little cooler than the ages that preceded them. What mattered more was dryness and drought. When the climate changes from wet and warm to cold and dry, plant life struggles to survive. Lightning sparks and high winds contribute to vast fires that consume large expanses of woodlands—and incidentally, woodlands were where humans’ apelike ancestors made their homes. This clearing of woodlands created an opportunity for grasses to spread and, following that, grazing herds to expand. What was a “bust” cycle for some species became a “boom” time for others. Those who lived in the forests and ate the plants of the forests could only survive at a fraction of the previous population size, with no time to shift gradually to other food sources.

In the sixth chapter, “Layover Limbo,” whose subject is “IQ and evolution’s package deals,” Calvin shows that when the brain increases in size, it does not do so “bump by bump.” Rather, an increase in size occurs across the entire brain, and one benefit likely comes along with a host of others. Calvin compares this to the package deal one gets when buying an automobile: The leather seats one wants require also taking power windows and a sunroof, even if they were not specifically desired. However, those unrequested extras may turn out to be useful at a later point in time.

Calvin discusses the differences between the skulls of Australopithecus, a vegetarian like the gorillas, and human ancestors. Grooves in the skull of Australopithecus show the presence of muscles to support the large teeth and chewing action needed to consume quantities of vegetable matter, while the absence of such grooves and presence of smaller teeth indicate that human ancestors were eating something else. Combining these physical differences with habitat conditions of grassland expansion, it can safely be assumed that their diet had shifted to the consumption of meat.

Eating meat was probably not a total innovation to these hominids. Animal protein is an important source of nutrients and fat an important source of energy. Chimpanzees, humans’ closest primate relatives, are opportunistic carnivores, meaning that they will consume small, helpless creatures that they come upon as they forage and will even band together at times to kill small creatures to eat. An interesting sideline of this practice is that it leads to chimpanzees sharing for mutual benefits beyond the food consumption of the moment. Whether they do this in the hope of sharing in another chimp’s future catch or to influence a sought-after mate, even the existence of “free-loaders” who never reciprocate does not cause sharers to cease this behavior. Early hominids had to learn to work together to capture larger animals and to share the catch that no one individual could consume before the meat spoiled. Those who had meat possibly shared with others who did not participate in the hunt to establish reciprocity in the future. Calvin quotes Frans de Waal, from his book, Good Natured: The Origins of Right and Wrong (1996), describing the irony that “human morality is steeped in animal blood”:

When we give money to begging strangers, ship food to starving people, or vote for measures that benefit the poor, we follow impulses shaped since the time our ancestors began to cluster around meat possessors. . . . Given the circle’s proposed origin, it is profoundly ironic that its expansion should culminate in a plea for vegetarianism.

Calvin travels down through Africa and examines the sites of ancient lakes and the presence of a common tool of Homo erectus, the hand axe. Its use is not completely understood. These stone tools, of a particular, symmetric, leaflike shape that is believed difficult to make, are not particularly suited as any sort of hand tool, being sharpened not only on the cutting edge, but also on the edge “the hand has to wrap around.” Many simpler tools would suffice for the uses that have been attributed to it. Calvin considers the hand axe and the congregation of game at shrinking water holes and comes up with a viable explanation, which also explains the presence of so many of these tools in the mud of ancient lake shores. The tools turn out to be an efficient way of bringing down large animals that have come to drink in herds. The momentum of the thrown stone, transferred to the animal, combined with the animal’s “pain flexion,” can defeat its ability to keep itself upright. The panic of the herd under attack could prevent the animal from getting back on its feet in time to escape the hunters.

The Little Ice Age, which occurred between the early Renaissance and the middle of the nineteenth century, gave rise to weather extremes that ruined harvests and caused famines. Although the average temperature changes were small, they caused colder winters and hotter summers. The famines might even have caused witch hunts, as people tried to understand why they were having trouble making a living as their parents had and looked for someone to blame. Perhaps it was easier to see witches riding the winds with evil intentions than to accept that the impersonal winds were the cause of the droughts that led to starvation.

The mechanism of climate and how it can go wrong is a complex subject. Painstakingly, with numerous charts, graphs, and even aerial photographs, Calvin explains the currents that carry warm water north from the tropics and cold water south in the Atlantic Ocean. This information helps to understand why Europe has such a mild climate even though it is farther north than regions in the United States that suffer through more severe weather. He delineates the physics of upwelling warmer waters and of winds evaporating water from top ocean layers until the salt left behind causes the colder waters to sink, forming a conveyor belt that sustains the current climate. The danger to this system posed by freshwater floods from melting glaciers, caused by global warming, is made clear through Calvin’s patient explanations of how global warming can lead to an ice age.

Going further, Calvin poses scenarios to describe the results of a global climate “flip-flop.” These possibilities, depending on whether humans do nothing to halt the change or try some of the methods he suggests, range from catastrophic population collapse and human misery to an undertaking that would cost, comparably, less than the construction of a medieval cathedral did in its time. Calvin’s assertion that this climate change is inevitable but also preventable raises this book far above the usual warnings of doomsayers who offer no practical solution to a problem once they have delineated it.

Sources for Further Study

Books and Culture 8 (May, 2002): 41.

Choice 40 (October, 2002): 319.

Discover 23 (June, 2002): 78.

Scientific American 287 (July, 2002): 91.

The Seattle Times, May 17, 2002, p. H25.

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