Did humans evolve concealed ovulation?

Humans do not exhibit visible manifestations of ovulation. In contrast, chimpanzee and bonobo females exhibit conspicuous swellings of their genital area during their fertile (periovulatory) period. This observation has led to the notion of “concealed ovulation” and it has been argued that this represents a distinctly human adaptation. Adaptationist scenarios proposed include promotion of paternal investment, confusing paternity to reduce the risk of infanticide, facilitating clandestine mating and female choice, and reducing female rivalry. Ovulation is unsignaled in many non-human primates, including the other great apes, gorillas, and orangutans. Thus, the null hypothesis that humans simply retain ancestral unsignaled ovulation remains viable, especially in light of the fact that self-reported patterns of mating behavior in humans do not seem to correlate with periovulatory periods. There is, however, a large and contentious literature on the potential existence of subtle ways in which women’s reproductive cycles influence behavior in both sexes. Of course, many human cultures across the globe have repeatedly evolved strong menstrual taboos, which could be considered cultural means of forcing women to declare their fertility status.