In short, diversity should precede disparity. The gradually increasing diversity of the lower taxa should ultimately result in the disparity of the higher taxa and the appearance of major new body plans. Phyletic gradualism Through the continuously gradual transformation of species this model predicts that the increasing diversity of the lower taxa should precede the disparity of the higher taxa. Lower taxon-level punctuations, however, require numerous transitional steps to produce the disparity of the higher taxa. This model also predicts that the increasing diversity of the lower taxa should precede the disparity of the higher taxa.
Disparity precedes diversity.
The initial appearance of virtually all phyla occurs with very low species diversity. Rather, the dominant pattern is top to bottom, contrary to theory. Disparity precedes diversity. We may acknowledge a central and surprising fact of life's history - marked decrease in disparity followed by an outstanding increase in diversity within the few surviving designs. In another article Valentine and Erwin review hypotheses as to the mode of origin of animal body plans for consistency with the fossil evidence.