Observations on the evolution of the genitalia and copulatory behaviour in male primates

Comparative studies of genital anatomy and sexual behaviour in male primates show that penile morphology and copulatory patterns tend to be more specialized in species which have a multimale or dispersed (non‐gregarious) mating system. The penis may be longer and more complex morphologically in such species. Copulatory patterns involving a series of intromissions or prolonged single intromissions are more common than in species with a monogamous or polygynous mating system. Elongation of the baculum occurs in species which prolong intromission into the post‐ejaculatory period. Sexual selection may have favoured the evolution of such features in species where females mate with a number of males rather than with a single partner. Relative testis size is also greatest under such conditions and larger testes occur in some non‐gregarious or seasonally breeding prosimians, as well as in anthropoids with multimale mating systems.