Fig. 3

Proportion of reports of repeated adaptive evolution versus null distributions in two key taxonomic groups. Morphological and physiological repeat adaptations among mammalian (a) and squamate taxa (b) as a function of phylogenetic separation. Shown as dashed bars are the proportion of species pairs at different phylogenetic separations across the entire super-tree for each group. These provide a general estimate on the proportion of species that have the potential to exhibit repeated evolution, if adaptive outcomes were not contingent and taxa were exposed to similar selection pressures