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. Early treatments of evolution presented our species' transformation from protohominid to Homo sapiens as an orderly affair, a matter of clear lineages and constant progress. That depiction, archaeologist Jeffrey McKee suggests, is a little too neat. Drawing on recent scholarly views of primate evolution and on chaos theory, he instead argues that coincidence, accident, and dumb luck are critically important components of our species' development. "Human evolution," McKee writes, "has been the product of many forces that together made us neither inevitable nor probable." The same holds true for other species; with all due respect to Lamarck, McKee adds, the giraffe came to have its long neck by a roll of the genetic dice--but a roll that lent the giraffe a competitive advantage over its shorter-necked browsing cousins, and therefore one subsequently reinforced by natural selection. Illustrating his argument with the well-worn "butterfly effect"--wherein a butterfly flapping its wings in Europe can produce a typhoon half a world away--McKee examines the role of chance in the origin and decline of species, emphasizing how unpredictable the dynamics of life can be, even within the bounds of natural laws. Within such disorderly circumstances, McKee observes, chance favors species that retain generalized features and behaviors. Whereas "the fossil record is littered with extinct primates that became too specialized," he writes, the ancestors of modern humans were broadly diversified, adapting to different niches and thriving in the bargain. Written well and at an appropriately general level, McKee's book offers a useful survey of current evolutionary thought. --Gregory McNamee The role of chance in human evolution is often underemphasized by those who think in terms of purposeful change. As this book usefully demonstrates, chaos theory can give us clues about our own evolution. McKee (anthropology, Ohio State Univ.) uses computer simulations to show how apparently minute changes in the initial makeup of a simulated population cause enormous changes in the population after many generations. Environmental change does not cause evolution, he says; natural selection acts either to preserve or kill off mutations but is dependent on mutations occurring by chance to make any changes. McKee, who has excavated fossils in South Africa, is also a proponent of the role of autocatalytic evolution, in which an initial evolutionary change is affected by feedback loops. This means that the survival and spread of a mutation is affected by its impact on the functioning of the organism within its species and in the current environment and that it in turn can affect the survival of mutations in other parts of the organism. Most of McKee's ideas are not entirely new, but his working out of their implications leads to important and sometimes unorthodox insights. His clear, informal, and anecdotal writing style makes sometimes complex ideas interesting a