The Evolution of Concealed Ovulation

Abstract

A hypothesis is presented that concealed ovulation occurs because of a hominid female tendency to avoid conception in biologically nonadaptive ways. This tendency was countered by natural selection by making ovulation virtually undetectable to women. The sequence of evolutionary adaptations culminating in concealed ovulation is most likely as follows. Olfactory, visual and pronounced behavioral cues to ovulation were lost to conspecifics. Coincidentally females evolved continuous receptivity, frequently copulating at times other than when ovulating. Females then lost conscious cues to their own fertility. This last step was predicated upon the acquisition of sufficient intelligence to associate copulation with pregnancy and sufficient self-consciousness to have reasons for wishing to avoid bearing children. The possibility of this sequence of events is supported by the finding, among primates, that the evoultion of receptivity outside the fertile period is not contingent upon loss of estrus. Physiological evidence suggests that women''s menstrual cycles are naturally irregular, compared to the cycles of other primates; women are unaware of rapid hormone changes occurring in their bodies at ovulation, but have numerous cues to impending menstruation, which is accompanied by less dramatic hormone changes; and the development of a simple, foolproof rhythm method of birth control is tedious and somewhat error-prone. These findings support the contention that ovulation has been actively concealed by natural selection. Anthropological literature establishes that women in primitive societies routinely attempt to control their reproduction. Many attempts seem biologically nonadaptive, being initiated for reasons such as fear of death, fear of pain or the inconvenience of having children. Such motivations among hominid females would have given natural selection ample reason and opportunity to suppress evidence of ovulation. Limited evidence suggests that men oppose certain female-initiated types of birth control. Such male opposition indicates that female attempts to control reproduction are sometimes not in the males''; biological (and perhaps egocentric) best interests. American women experience the greatest conscious desire for intercourse just following and/or prior to menstruation. Psychoanalytic evidence suggests that women are most loving and receptive near ovulation, and other evidence indicates that a peak of copulatory activity may occur at ovulation. The specific cues that result in this phenomenon are unknown.