Comparative methods for studying primate adaptation and allometry

A well-known comparative biologist was once asked by a field biologist whether the latter's detailed and painstaking field study of orangutan behavior, carried out over many years, qualified as an example of the comparative method. No, replied the comparative biologist, that's an anecdote. The reply is somewhat harsh, as useful comparisons can be conducted both within and across species. The reply does emphasize, however, that analysis of patterns across species is fundamental to the study of adaptive evolution, particularly when variation needed to test hypotheses is present only at this interspecific level.(1-5) Examples in primatology include the occurrence of female sexual swellings in species with habitually multimale, rather than single-male, breeding systems,(6,7) the relationship between polygynandrous mating and relatively large testes size,(3 8) and the association between brain size and social group size.(9) Thus, in many cases, interspecific variation is required to test adaptive hypotheses(10).