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Did human evolution proceed in an inevitable fashion? Can we attribute our origins solely to natural selection, or were more mischievous forces at work?

These are the questions investigated by anthropologist Jeff McKee. He argues that if we were to wind back the clock to our split from ancestral apes, evolution would proceed differently. Ever since our ancestors first stood up on two feet, natural selection undoubtedly was an important factor in guiding human evolution. But McKee shakes the standard notion that natural selection steered early hominids toward particular environmental adaptations. The fossil remains of our ancestors reveal a different story one of an adaptable hominid with no particular direction. It becomes clear that the evolutionary road to Homo sapiens was not paved solely by natural selection; indeed, there was no road to follow. There was just a dim path cut out by prehistoric coincidences and contingencies. Had any link in the evolutionary chain of events been slightly different, then our species would not be as it is today . . . or our ancestors may not have survived at all.

With equal doses of humor and awe, McKee illustrates how the chain of evolution has been riddled by chance, coincidence, and chaos. He uses familiar examples, noting that many of us exist as individuals because of chance meetings of our parents. From the present back through prehistory, chance is at the heart of our creation is chaos. The classic example of chaos is the butterfly effect: a single butterfly, flapping its wings, causes a tiny change in the atmosphere, which in turn amplifies to affect the course of storms on another continent. McKee ties such examples of unpredictability to fossil evidence and computer simulations, revealing the natural coincidences that shaped our evolution. Although chaos exacted an evolutionary price by limiting the powers of natural selection, it also made us what we are. One can only conclude that human beings were neither inevitable nor probable.