Menstrual cycle and social behavior in vervet monkeys.

We assessed the relationship between social behavior and the menstrual cycle in 11 adult female vervet monkeys (Cercopithecus aethiops sabaeus) living in an established, stable social group. The findings indicated that fluctuations in ovarian steroids are accompanied by behavioral changes in vervet monkeys. A significant increase in aggressive action, avoidance of social overtures, and retreats from threat occurred during the late luteal phase. However, the social environment can greatly affect behavior independent of the phase of the menstrual cycle. The 10 nondominant (or subordinate) individuals not only exhibited behavioral changes across their own menstrual cycles, but also were responsive to the dominant female's cycle. During the dominant female's late luteal phase, subordinate females significantly increased aggression and decreased social activity. Some of behavioral patterns in female vervet monkeys are therefore relatively independent of direct hormonal modulation and support the contention of the dominant female as the driving force for behavioral changes related to aggression and social interaction. The differential effect of hormones and social status and other environmental factors on behavior has not been critically evaluated in human studies of the premenstrual syndrome. The present study suggests that it is important to assess which behavioral patterns in women are hormonally mediated and which are dependent on the environment.