Ann Austin: recommended link
Function of the female breast
The function of the mammary glands in female breasts is to nurture the young by producing milk, which emanates from the nipples during lactation. However, zoologists point out that no female mammal other than the human has breasts of comparable size when not lactating, and this suggests that the external form of the breasts is connected to factors other than lactation alone.
Mammary glands
The mammary glands that secrete the milk from the breasts actually make up a relatively small fraction of the overall breast tissue. It is commonly assumed by biologists that the real evolutionary purpose of women having breasts is to attract the male of the species; that, in other words, breasts are a sexually dimorphic, or secondary sex characteristics. Some biologists (notably Desmond Morris) believe that the shape of female breasts evolved as a frontal counterpart to that of the buttocks, the reason being that whilst other primates mate in the typical piggy-back position, humans are more likely to successfully copulate mating face on. A secondary sexual characteristic on a woman's chest would have encouraged this in more primitive incarnations of the human race, and a face on encounter would have helped found a relationship between partners beyond merely a sexual one.
Recessive jaws ... bigger breasts!
Others believe that the human breast evolved in order to prevent infants from suffocating while feeding. Since human infants do not have a protruding jaw like our ancestors and the other primates, the infant's nose might be blocked by a flat female chest while feeding. According to this theory, as the human jaw became recessed, so the breasts became larger to compensate.
Copyright: This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on Breasts.