Hans Baldung – The Seven Ages of Woman
Like all higher primates, we have sex for pleasure, even when women are not ready to conceive. Chimpanzees and many other primates have an area of bare genital tissue that swells and colours during ovulation, advertising a female’s fertility. In our species, however, a woman’s readiness to conceive is hidden even from herself. Some biologists think that this “concealed” ovulation in women to make men more faithful – if ovulation was signposted, a man would safely be able to neglect his partner during her infertile period in the knowledge that any offspring would be his. According to this theory, concealed ovulation and sex for pleasure are among a suite of adaptations that cement the bond between couples and encourage fathers to share in the childrearing process.
However another possible explanation for concealed ovulation is our upright posture. when humans became upright, the external female genitals changed position and became concealed between the legs. Upright posture may also explain the human male’s long penis.