Numbers of gene duplications in two- to eight-member families. A duplication was dated prior to one of the three a major cladogenetic events (the animal–fungus divergence, the coelomate–nematode divergence, and the deuterostome–protostome divergence) if its occurrence prior to the event was supported by a significant internal branch. Chi square tests of the hypothesis that the proportion of duplications prior to a cladogenetic event differed from that inDrosophila: (***) P < 0.001. Numbers of duplication events were as follows: Caenorhabditis elegans, 463; Drosophila 567; human, 1760.