The distinguished Harvard biologist Ernst Mayr set out to write a ""developmental"" as opposed to a ""descriptive"" history of biological thought--and in close to a thousand pages, he covers millenia of growth and development, change and maturation. In conclusion, he discourses on the potential of a ""science of science."" An ardent student of the history of science, Mayr takes pains to dissect changes in concepts and in the meanings of words like classification, diversity, and evolution. His work is divided into three parallel chronological sections. The first, ""The Diversity of Life,"" gives Mayr a chance to deal at length with an area of biology which long dominated the field--systematics and classification--and to which he himself has made substantial contributions. He is the chief architect of the notion of ""biological"" species, defined in terms of the exclusive ability of group members to breed successfully among themselves. Section two, ""Evolution,"" covers the more familiar territory of biological thought--from pre-to-post-Darwinian times--which climaxed in the ""evolutionary synthesis"" (about which Mayr and William Provine have recently written). The synthesis refers to a period from 1936 to 1947 when a consensus developed among naturalists, population specialists, and geneticists that evolution by natural selection accounted for the gradual descent of varying populations whose diversity reflected environmental and chance factors that were wholly in keeping with the findings of genetics. The final section, ""Variation and Its Inheritance,"" takes a closer look at the gene and at developments from Mendel through Watson-Crick. Mayr's writing is prolix and he is also required, by the three parallel chronologies, to constantly re-introduce Aristotle or Buffon or Linnaeus. His own biases--an antipathy toward mathematicians, for example--sometimes seem extreme. And one would have welcomed his thoughts on current controversies--such as the challenge to gradualism posed by Mayr's former student, Stephen Jay Gould. (As for ethology or behavioral biology, we are told there are works in progress.) Nonetheless, Mayr has done nobly at assembling a comprehensive history of ideas in biology, with sufficient detail about individual contributions to make the work a valuable reference.