Not for the first time has Goya's inspired quote, ""The dreams of reason bring forth monsters,"" inspired a text. In Pagels' case, it is the epigraph to a concluding chapter--a coda to a volume that celebrates a new age in science. That chapter allows Pagels to speak of fragile, fallible reason as the link between the moral values and the deep primitive feelings that shape human behavior. The search for an absolute guide to action--be it religion, philosophy, ideology or science itself--is doomed because ""science is a selective system. . .subject to what we discover in the real world."" This is sober and satisfying commentary on the vaunting ambition so often expressed by scientists since the Enlightenment and, indeed, by many of the people described in the book. These are the new mathematicians and physicists--and growing numbers of biomedical and behavioral scientists--who are exploring complexity, using the computer as a research tool. Theirs is a world of nonlinear systems, focusing on modeling real-world phenomena that lie somewhere between predictable noninteresting patterns and chaos--the kind of world exemplified by weather and turbulence, by economic systems, and by the behavior of brains, immune systems, and the evolutionary process itself. Pagels has digested the literature and guides the reader through the science of complexity, steering past shoals of artificial intelligence and Chomskyian linguistics, genetic programs and the mind-brain problem. It is to his credit that he has mastered so many applications; knows so many of the innovators. However, covering fewer areas in greater depth might have better served reader comprehension. As it is, when Pagels injects personal history and incisive commentary, the book goes beyond mere survey and achieves its own level of interesting complexity.