Effects of an oral contraceptive on sexual behavior of chimpanzees (Pan troglodytes).

Behavioral and physiological effects of a combined oral contraceptive (OC) were studied in chimpanzees for comparative purposes related to (i) the ambiguity surrounding the effects of OCs on the sexuality of humans, (ii) the close biological relationship between chimpanzees and humans, especially with respect to endogenous sex hormones and sexual behavior, and (iii) the relatively greater behavioral sensitivity of the chimpanzee to changes in sex hormone levels such as those that accompany the use of OCs. Two different types of pair tests and detailed behavioral assessments were used to differentiate the hormonal effects of female behavior from social effects imposed by the male. Anogenital swelling and copulation were reduced during OC cycles, but the effect of the OC on copulation was directly related to the social and sexual relationship of the pair during natural cycles. The more compatible and more frequently copulating pairs in the natural cycles continued to copulate during the OC cycles, albeit at reduced rates, whereas the less compatible and less frequently copulating pairs ceased copulating altogether when the female received the OC. There was no independent effect of the OC on ejaculation per se. Both male and female sexual initiative were reduced in the OC cycles, but female responsiveness to male sexual solicitations and direct copulatory attempts were not affected. Data indicate that despite generally adverse effects of the OC on certain physiological and behavioral dimensions of sexuality, social factors ultimately determined the degree of response to the OC.(ABSTRACT TRUNCATED AT 250 WORDS)