SYNOPSis. The ground-plans of higher metazoans seem to have originated chiefly in two waves, one near 700 million, the other near 580 million years ago. The first wave, involving the origin of the coelom, was probably associated with invasion of the substrate and the evolution of an infaunal community, while the second involved a reinvasion of the sea-floor surface and the development of an epibenthic fauna, for which skeletonization was a common adaptation. Each of these waves seems to represent adaptations to patterns of environmental variability?that is, they originate as adaptive strategies. Later waves of diversification tend to involve lower taxonomic categories but nevertheless appear to have been associated with changes in adaptive strategies. The fossil record of the marine biota suggests that there have been waves of di? versification of higher taxa, just as there have been waves of extinction, at times in the past. Some of the waves of extinction can be explained by environmental events that lead to a lowered capacity for species diversity, and in theory this capacity is partly related to adaptive strategies. When most or all of the species of a given higher taxon have followed an adaptive strategy that proves unfavorable after an environ? mental change, then the entire higher taxon is likely to become extinct. When sev? eral higher taxa disappear at about the same time, it is possible that they shared similar strategies. When waves of higher taxa appear in the fossil record at about the same time, it implies some special change in the biosphere that has stimulated or at least permitted such a diversification. Numbers of higher taxa (orders and above) of marine or? ganisms appear especially in Ediacaran time, during the Cambrian, during the Or? dovician, and during the early Mesozoic. It is therefore postulated that environmental changes at these times created the oppor? tunity for novel adaptive strategies in many lineages, and that evolution to develop such strategies gave rise to novel body plans that became the bases of higher taxa. ADAPTIVE STRATEGIES AND THEIR COMPONENTS