Did you add a word to the title? Like a subliminal message, ""recapitulates"" will come reflexively to the mind of readers exposed to a biology course at one time or another. And indeed it is the point of this grand tome, a tour de force, to resurrect and revitalize--albeit with altered meaning--a concept that sent 19th-century scientists to the battlements. The argument that the German anatomist Ernst Haeckel formulated as a biogenetic law was that in embryological growth (ontogeny) organisms repeat the forms achieved by adult species which appeared earlier in evolution (phylogeny). Thus, the human embryo shows the gill slits of an adult fish at a certain stage. Developments in Mendelian genetics and biology demolished the theory. Yet the tantalizing analogy was never far from the surface, as Gould amusingly notes: when queried, colleagues would, figuratively, look both ways and whisper that they did think there was something in it. Gould's ""something"" has to do with the timing of development. He supports the neoteny theory that species may retain juvenile traits in maturity. Retardation in human evolution may account for the hypertrophy of the brain, erect posture, frontal copulation, and a host of other treats frequently adduced as quintessentially ""us."" These ideas are presented in detail and scholarly length. There is a rich historical development as well as the appeal to contemporary geneticists and molecular biologists who have traced the chromosomal similarities between apes and humans or who have studied regulatory genes and the timing of gene expression. The more sophisticated yearn for a skeleton key (for which Gould's popular writings, above, may help enormously). Nevertheless the ideas are beautifully worked out and elegantly expressed. It will be exciting to see whether once again biologists rush to the battlements.