A fascinating and detailed examination of the evolution—and occasional devolution—of sexuality in microorganisms and more complex forms of life. Margulis and Sagan trace sex from its inauspicious beginnings in bacteria threatened by ultraviolet radiation to its intimate relation with the origin of mitotic division of nucleated cells. The origin of meiotic sex through cannibalism followed by centriole reproductive tardiness and the connection of cell symbiosis to sex and differentiation are explored. “The authors have not only given us a new and exiting scenario for the evolution of sex, but have also provided us with critical ways in which we can test their hypotheses. . . . This is a stimulating book that is sure to invoke criticism and discussion; I strongly recommend it.”—Symbiosis “The book is well organized and well written, leading the reader from one thought to another almost effortlessly. Background information is presented to aid those of us who are not experts in this field, and a glossary is appended. The book could be used at all levels of study, from interested undergraduates in general biology though postdoctoral students of genetics and evolution. I recommend this thought-provoking book to you for both your enjoyment and your enlightenment.”—Richard W. Cheney, Jr., Journal of College Science Teaching “This book, undoubtedly controversial, is a thoughtful and original contribution to an important aspect of cellular biology.”—John Langridge