A couple of weeks ago I wrote a post about the function of the foreskin and why it might exist in the first place. There are lots of things we don't understand about the human body and why the female breast is the way it is, is one such mystery. What then is the great mystery about boobs? From Wikipedia's page on breasts:
Zoologists point out that no female mammal other than the human has breasts of comparable size when not lactating and that humans are the only primate that have permanently swollen breasts. This suggests that the external form of the breasts is connected to factors other than lactation alone.
Look at the two pictures of the adult female chimpanzees. The first shows that female chimps normally have a flat chest (which only swells when breast feeding). The second picture shows what happens to a female in oestrus - this female is ready to reproduce and is advertising this fact to males (hence the very prominent swelling in her rear). Since we share a common ancestor with chimpanzees, why do human females not get this same swelling and why are human females usually endowed with permanently swollen breasts which develop at puberty?
Nobody has a definitive answer to these questions, but what has been suggested is certainly thought provoking. The two main positions fall into breasts as a replacement for the engorgement seen in chimpanzees or as a means of concealing fertility, thus ensuring constant attention from male partners. From How Mate Choice shaped Human Nature:
female humans have greatly enlarged breasts and buttocks, a greater orgasmic capacity, and continual `sexual receptivity' throughout the monthly cycle. Many of these traits show hallmarks of having evolved under the capricious power of sexual selection: they are uniquely elaborated in our species, show considerable sexual dimorphism, are grown only after puberty (sexual maturity), become engorged and displayed during sexual arousal, are manifestly valued as sexual signals, and are selectively elaborated through ornament and make-up (Miller, 1993; Morris, 1985). Such traits probably evolved both as indicators (of fertility, viability, age, health, and lack of infestation by pathogens and parasites) and as aesthetic displays (that play upon pre-existing or co-evolved perceptual biases).
Permanent enlargement of breasts and buttocks is also fairly effective at concealing ovulation (Margulis & Sagan, 1991; Szalay & Costello, 1992). Females who do not reveal their menstrual or lactational cycles may benefit from male uncertainty by being able to solicit male attention and investment even when they are not really fertile: "From hairy, flat-chested ape to modern buxom woman ... males were kept guessing about when females were ovulating" (Margulis & Sagan, 1991, p. 96). More generally, the loss of a specific estrus period, combined with `concealed ovulation' and `continuous sexual receptivity', may have allowed females to attract more continuous attention (e.g. protection, provisioning, social support) from males even when they were not ovulating (Alexander & Noonan, 1979; H. Fisher, 1982; Hrdy, 1981, 1988; Hrdy & Whitten, 1987; Tanner, 1981).
Alexander and Noonan (R7) argue that concealed ovulation, and the breast as a permanent signal of receptivity, enabled a female to hold on to a mate by reducing paternity certainty at the same time as inviting sexual receptivity, making it difficult for a male to know when she is on heat and thus having to stick around. Receptivity is then both an invitation and ‘sex as a weapon’ to enforce male resourcing compliance. Jared Diamond (R161) calls this the ‘daddy-at-home theory’. Diamond argues that a woman had to conceal her ovulation; otherwise her husband would only stay with her when she was exhibiting signs that she was fertile. The rest of the time, he would be out trying to find other women, who were exhibiting signs that they were sexually ready His absence would be detrimental to his children, and by concealing her ovulation, a woman convinced a man to stay by her side and make love to her throughout the month, so that he could be sure he was fathering the children she bore. However Shlain (R617) notes that several flaws and inconsistencies, weaken the argument that promotes sex as the glue holding human relationships together. If sex served the purpose of ensuring the durability of the human parenting commitment, then parents should become more ardent in their lovemaking following the birth of a baby. Instead, the opposite occurs. Both parents routinely report a sharp fall in their respective libidos. Barbara Smuts adds the ironical twist of females tolerating male mates to protect against coercion by other males, thus forcing males to accept these bonds even when they involved lower-ranking males (Pusey R540). Wrangham (R742) has even speculated that pair bonds may relate to food guarding, with the establishment of cooking.
Stated in brief, I believe that upright walking hid females’ engorgable estrus skin between their legs; walking itself both required buttock muscles and hid the female genital opening - an important focus of sexual signaling in primates; the new buttock area became denuded of hair to compensate for the lost sexual signal; and the bare buttocks were mimicked around the front, in the form of bare breasts, [and a pubic triangle of hair against a bare background]. That is, nakedness developed as a form of sexual signaling to compensate for the disappearance of estrus skin, which had formerly performed that function. The emergence of nakedness was thus not a question of losing hair but of extending areas of sexual skin. This process culminated through sexual selection within a cultural environment-clothes and cosmetics enhanced and selectively covered the areas from which hair was lost, and encouraged it to be lost over yet wider areas. In my view, therefore, we have never been truly naked apes (R661 34).
I don't know which position I favour more. The rather bizarre engorgement of a fertile chimpanzee is certainly a strong sexual signal and it seems odd that human females don't have such a thing. Since beauty isn't an objective measure, I cannot believe that the human females today don't have such a gorging for aesthetic reasons. But the real answer will probably remain an unexplained mystery because of the inability to go back in time and investigate what selection pressures influenced our human ancestors. Plus fleshy breasts don't leave good fossils (and they didn't have under-wired bras in the the distant past). Whatever their function let's give a cheer for breasts. I for one, have fun contemplating them!Go Top