One hypothesis postulates that the breasts grew as a frontal counterpart to the buttocks as primates became upright to attracting mates, a model first developed in 1967. Humans are the only primates whose female members have permanently enlarged breasts after the onset of puberty the breasts of other primate species are enlarged only during pregnancy and nursing. Nipple and breast stimulation of women are a near-universal aspect of human sexuality, though nipples in males are not as sexualized.
5 Lactation, re-lactation and induced lactation.
