The mother-son team that brought you Microcosmos: Four Billion Years of Microbial Evolution (1986--not reviewed) now tackle the age-old theme of the origin of sex. Margulis (Biology/U. of Mass. at Amherst) and Sagan (Biospheres, 1990) choose to do this in a particularly florid style, using the image of an androgynous stripteaser who displays facets of sexuality at different ages and stages of evolution. But that's not all. The book is (a) a kind of postfeminist review of all the sociobiological hype of the 70's and 80's. This time, however, instead of crying foul at the macho writers who wrote of breasts and buttocks and pair-bonding and said it made good genetic sense to be promiscuous, to rape, blah-blah, the authors rehash all the old theories with mild caveats that genetic predestination is not destiny. The book is also about (b) the evolution of the penis (and the possibility that size and length may confer the advantage of depositing sperm higher up in the vagina with better chances of reaching an egg than a rival's ``sperm competition''); (c) Freud, the French deconstructivists Lacan and Derrida, and phallic symbolism; (d) neoteny; (e) mating styles of the great and small; (f) the reptilian brain that presumably lives on in all of us; (g) the origin of language and time.... Finally, we learn that the usual explanation that sexual reproduction increases genetic variation, and thus the odds of adapting to changing environments, is not sufficient: cloned or fissioned creatures also differ. The answer then? Sex is an ``unkickable genetic habit''--passed on from the bacteria who knew all about passing genes back and forth, and the protists (like the amoeba) who cannibalized each other to survive. This latter theme is by far the most well developed, drawing upon Margulis's special knowledge and insights into symbiosis in cellular evolution. The rest can be described as flights of fact, fancy, and fantasy with no clear distinction.