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.”
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...
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