Sexual behavior of captive lowland gorillas

Abstract

One of the more enduring issues in the study of sexual behavior concerns the degree to which this activity is regulated by hormones. In his early review of this subject, Beach (1942) concluded that, across phylogeny, species with relatively greater encephalization developed greater cognitive control over behavior and a decreased behavioral dependence on hormones. At the time Beach proposed his hypothesis, there had been few systematic laboratory studies conducted on the more advanced species and among the apes, only the chimpanzee having been investigated (Yerkes and Elder, 1936; Yerkes, 1939). The results of these latter studies indicated that chimpanzees, in general, copulated at all phases of the female's sexual cycle, but also that the preponderance of sexual activity occurred during a 10-day midcycle period of maximal female genital swelling. The concordant increase in copulation with genital swelling suggested that hormones were influencing sexual behavior of this species, whereas the occurrence of copulation at phases other than.midcycle indicated at least some degree of behavioral independence from hormones. Therefore, based on the chimpanzee data, the great apes appeared to display an emancipation from hormonal regulation of sexual behavior commensurate with their taxonomic affiliation with man. Clearly, evaluation of the phyletic status of a taxonomic family, such as the great apes, requires data on more than a single species in order to define which of the characteristics of interest pertain to the family as a whole and which pertain only to the particular species studied. There is still a paucity of information in the literature related to sexual behavior of the other two great apes, gorilla and orangutan, and that which pertains to the gorilla was derived primari-