Roger D. Launius 2007-06-17
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Human evolution is one of the great detective stories of the twenty-first century. How did this species, Homo sapien sapiens, come to be? Our written record provides some details for only about the last 10,000 years, but what about the millions of years on Earth beforehand? Charles Darwin's rock-solid theory of natural selection, while attacked from the political and religious right as unable to explain the "miracle" of life in the universe without reference to God's creation, remains at the center of all explanations that take a scientific perspective on the subject. William H. Calvin, on the faculty at the University of Washington's School of Medicine, offers in "A Brain for All Seasons" a modification of Darwin's theory that is both illuminating and reasoned. He argues that while Darwin thought in terms of eons of time and slow progression across thousands of generations, some evolutionary processes might be more immediate and striking.
Specifically, Calvin asserts that the capacity and complexity of the human brain grew significantly in response to cataclysm on the Earth. Cycles of radical and abrupt climate change, warm-and-wet versus cold-and-dry, help to explain the current state of human evolution. Ancient humans were driven to adapt within a few generations to abrupt climate change, a set of cycles between ice ages and warm seasons, forcing biological as well as other changes on those who survived (and probably few did). These "whiplash" climate shifts, as Calvin calls them, meant that those most adaptable survived and others did not. One major aspect of adaptability is brain power and reasoning. While not exclusive to Calvin, other scientists have made this case effectively, "A Brain for All Seasons" offers a reasoned, accessible explanation of how humanity came to be as it is today. It also offers a cautionary note about the potential for future abrupt climate change and what it might portend for the future of humanity. Wars over land and resources appear almost a certainty, he contends. Widespread starvation and death will also result. And again, those with the most adaptability will survive.
William Calvin's analysis is erudite and thought-provoking. It is also highly entertaining. Written as a travelogue that stretches across the globe, especially Africa and the Arctic, "A Brain for All Seasons" serves as an entrée for a lay audience into the world of paleobiology. Calvin does a good job of speaking to that broad audience, but as is the case with most books that seek to communicate scientific knowledge to non-scientists this one sometimes oversimplifies and overstates the evidence. It should be read, as should all books, with a critical mind, something that I'm sure William Calvin would appreciate. Taken altogether, however, it is a useful starting point in understanding how humans evolved from the distant past.
