ABSTRACT. Adolescent females of 11 primate species display exaggerated versions of the cues to sexual cycle state or fertility which are displayed by adult females: anubis baboons; geladas; Assamese, Barbary, crab-eating, Japanese, and stump-tailed macaques; patas monkeys; gorillas; and humans. These cases are briefly described and a variety of hypotheses is presented and evaluated to account for the adolescent exaggeration. Such exaggeration may be a super-normal sexual stimulus, a barrier to cross-species hybridization, a helpful prop in female:female competition, a passport for transfers, an insurance policy where unpredictable changes of circumstance are likely, or a nonadaptive side-effect of some other phenomenon. The transfer and unpredictability hypotheses seem to apply to the largest number of species, including humans.

Male chacma baboon (Papio ursinus) sexual arousal response as gauged by the coagulated seminal emissions resultant from masturbatory activity was experimentally assessed. Males were initially exposed to an ovariectomized female prior to and during daily oestradiol benzoate treatment. Males were then re‐exposed to the same female prior to and during the wearing of a thermoplastic model of a swollen female perineum. A total of eight different colours were sequentially applied to the model. It was only the red model that elicited a response similar to that shown to the oestradiol‐treated female. The behavioural data collected from the stimulus female supported the view that it was model colour that determined the differential male response.

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Behavioural and hormonal data were collected throughout pregnancy in captive rhesus monkeys. Heterosexual pairs observed in daily time-limited mating tests showed two distinct periods of increased sexual interaction, as measured by the incidence of ejaculation. One period was coincident with the preovulatory oestradiol peak, while the other occurred between the 6th and 10th weeks of pregnancy. The positive relationship found during the menstrual cycle between the ratio of circulating oestradiol: progesterone and degree of sexual activity continued for the first 8 weeks of pregnancy. However, sexual activity ceased in the second half of pregnancy despite a continued high oestradiol: progesterone ratio.