Numbers of gene duplications in three family size classes (two- to three-member families, four-member families, five- to eight-member families). A duplication was dated prior to one of two major cladogenetic events, (a) the coelomate–nematode divergence, and (b) the deuterostome–protostome divergence, if its occurrence prior to the event was supported by a significant internal branch. Chi-square tests of the uniformity across family size classes of the proportion of duplications prior to the cladogenetic event : (**) P < 0.01; (***) P< 0.001.