Figure 1.

Models of the evolutionary history of a group of species with interspecific variation in a character that may affect speciation and extinction rates of lineages. (A) No higher order effect. Transitions in the character state of this character occur commonly. Species with these traits (bold lines) do not form monophyletic groups. Species selection does not produce any observed pattern of trait variation among fossil assemblages. (B) Very few (one) transitions in character state. Different character states affect species’ origination rates. Species with similar traits form monophyletic groups. Species selection in this case could change the frequency of this trait among species over time.