This review deals with possible central and peripheral effects of androgens upon primate aggressive behavior. One problem that clouds interpretation of experimental work is that measurements of dominance have often been employed, such as competition tests for food and water. Such measures often do not correlate with those obtained by quantifying aggressive interactions. It should be remembered that very few of the 188 primate species have been studied experimentally and that great behavioral and physiological diversity occurs within the order. Therefore, generalizations about the effects of androgens upon aggressive behavior in primates (including man) should be made with caution. Testosterone has an organizing influence upon the foetal brain of rhesus monkeys and may affect the development of neural mechanisms which govern aggression in males. More data are required on primates, however, since rhesus monkeys show some important differences from rodents as regards the effects of androgen upon sexual differentiation of the hypothalamus. In future, marmosets may provide a suitable model for such studies, because there is evidence that sexual differentiation of brain by androgen occurs postnatally in these monkeys. At puberty, male primates show a variety of behavioral changes and, during adulthood, males of seasonally breeding species may be more aggressive during the mating season, when testosterone levels are maximal. This does not indicate a causative relationship between testosterone and aggressive responses, because castration and androgen treatments have little effect upon aggression in prepubertal or adult males of several primate species. Androgens have pronounced effects on sexual responses in adult male monkeys, but their central effects upon aggression are much less important than among rodents. Elec trical stimulation of hypothalamic pathways has been employed to evoke aggressive behavior in marmosets and rhesus monkeys. In the rhesus, preliminary evidence indicates that such pathways show some sensitivity to androgens. In rodents it is known that these areas are richly supplied with monoaminergic neurons, which play an important role in aggressive behavior. There is little evidence on primates, however, and this remains a crucial topic for future research. Peripheral effects of androgens should also be considered. Many prosimians and New World monkeys use scent‐marking behaviors and, in males, androgen‐dependent chemical cues may be involved in sexual recognition and territorial behavior. This possibility awaits investigation. Finally, plasma testosterone levels may alter as a function of aggression itself; thus levels decrease if male rhesus monkeys are defeated by conspecifics. This might occur because neural events associated with giving (or receiving) aggression also influence pituitary function and hence alter gonadal testosterone secretion. Theoretically, it is possible that such changes in circulating testosterone might affect aggressive behavior via a feedback action on the brain, but ...

Behavioural interactions between parents and their developing offspring were studied in 13 captive groups of Owl monkeys. The male parent plays an important role in carrying the offspring and in ensuring the development of its independence. Older siblings also carry infants, but this behaviour is infrequent and age or sex differences are not measurable. Patterns of parental behaviour in Owl monkeys are compared to those observed in other monogamous primates and their adaptive significance is discussed. Some experimental studies of clinging positions in infant Owl monkeys are also described. The newborn possesses some innate ability to cling in a distinctive ventro‐lateral position upon the mother's body.

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Repeated measurements of plasma testosterone (T) were made in 56 male marmosets from the day of birth until 300 days of age and in 44 adults (>3 years). The resulting profile of plasma T during postnatal development shows higher levels during infancy (1–90 days) followed by a nadir between 100 and 170 days and then a progressive rise in T during puberty. Although T levels of up to 21 ng/ml were measured in infant males, mean levels (±SEM) were 5.4 ± 0.6 ng/ml (days 1–10), declining gradually to 1.7 ± 0.1 ng/ml (days 100–110). No increase in mean T levels between 15 and 100 days was identified, and the onset of puberty was earlier in some males than measured previously in this species.