Homosexual behaviour and female‐male mounting in mammals—a first survey

Information from the literature is given on the presence or absence of homosexual behaviour and female‐male mounting in 125 species of mammals, both captive and wild. Such behaviour occurs in the male and often female young of many species soon after their birth. It is more common in young, often in play, than in adults. Adult homosexual behaviour is widespread in male and female mammals (recorded in 63 and 71 species respectively), but common in few species. In males it is most likely to be correlated with dominance and thus to occur in species with hierarchies such as terrestrial monkeys and members of the sheep and goat tribe. In females it is often correlated with sexual condition; a female in heat most often mounted another female, and one in heat was next most likely to be mounted by another female. Anoestral females rarely mounted other anoestral females. Females of 43 species mounted males, which often excited them sexually. Captive mammals tended to mount animals of the same sex more often than did wild ones when comparative data were available. Domestic animals also mounted more man did wild ones, with several exceptions. Some phylogenetic groups of animals displayed similar degrees of homosexual mounting, but there was often considerable variation between closely related species. Nor could homosexual mounting be always correlated with the social structure of a group. The four reasons for, or contexts of, homosexual and female‐male mountings were social play (in 34 species), aggression (19 species), sexual excitement (36 species), and physical contact—non‐play (30 species). This last category included a state of tension, getting attention, greeting, grooming, caressing, reassurance and appeasement. There was some overlap between categories. Homosexual pair‐bonds occur in captive mammals and have been observed throughout the year in non‐captive female Japanese monkeys.