Our "modern" bodies are a model approximately 30,000 years old because the basic design has not changed significantly in the past 30,000 years. For one thing, we still have sexual identifiers that our ancestors found useful throughout history for finding a mate to create an ongoing relationship.
For example, breasts are one main part of women's bodies used to convey sex identification. In ancient times it was very prudent to identify an approaching stranger from a distance and know if one was going to need to fight a potential male enemy or get to have a "roll in the grass" with a new woman.
Women's breasts have been conveniently used to identify the difference between men and women throughout history, at least in most cultures still today. Interestingly, we see that women's breasts are larger than necessary to feed children. And they do not reduce in size much after the children are no longer feeding on them, as all animal breast do.
An eight hundred pound gorilla and other large mammals have much smaller breasts than human females, yet, the animals feed their young very satisfactorily. All primate females, except humans, are flat-chested until the female is producing milk for her new-born baby.
Ingrained in women's DNA is a drive to show they are female and are good candidates for producing children. These signs demonstrating femininity for breeding are well rounded breasts, narrow waist, symmetrical body features, and good healthy hair, teeth, and skin. Without that female drive to reproduce, humans may have gone extinct long ago. Thankfully, women unconsciously want to appeal sexually to men and are competing with all other women for the best man's attention. This "game" has been going on throughout our history as a species and has worked well as evidenced by our growing population in every corner of the planet.
Moreover, the human female breasts remain protuberant and change little in overall size after the child stops nursing because the breasts contain approximately 4% of the body's fat. Although the primary purpose of breasts is for feeding the offspring, human female breasts do not need to be as large as they are generally. The reason for being unnecessarily large comes from their second purpose: Gender Identification.
A secondary purpose for women's breasts is sexual identification. Large breasts are generally more sexually appealing to men, and also served as a species and gender identifiers for the past millions of generations. Women's larger than necessary breasts we men can most likely be thankful to men's ancestors' consistent preference for that hemispherical shape on women's body. It appears this large rounded shape was prized and selected for through natural selection by most ancient men --as well as many modern men today! Women throughout history with these male-preferred characteristics were in higher demand and undoubtedly had more offspring.
It is obvious that women today recognize the value of breasts as signals of femininity. A multimillion dollar breast enhancement industry is thriving. Since 1963, silicon gel implants have been used to provide women with perfectly shaped hemispherical breasts. This fact says much about how many women feel inadequate because of their small breast size or shape. Furthermore, in recent times it has become fashionable to surgically enhance even lips, checks, and buttocks to make them appear more rounded.
One of the reasons men may be so attracted to women's breasts is chemical. There are apocrine glands around the breast nipple, as well as under the arms and in the pubic area, that secrete erotic odors. These feminine odors cause men's brains to release an avalanche of male sex hormones that make men feel strong, pain-free, and excited.
If two breasts are good, are more better? About one in every 200 women has a third breast, and even more rarely: four. The most in medical records were 5-pairs on a French woman in 1886. These extras are seldom more than a small nipple or a fat mound, much like a young girl's breasts just developing. Extra breasts are evidence of DNA still hanging around from our animal ancestors who gave birth to litters of more than two offspring at a time .
In most western cultures women dress to show they are female and are good candidates for producing children. This is a powerful and deep need in women's DNA and comes from women's millions of ancestors throughout history.
Women's strong need to show they are good candidates for making babies is unconscious but always there during the childbearing years - even when they consciously say differently! One main way of displaying a woman's need for producing offspring is her showing that she has breasts.