As you may have noticed, heterosexual men seem to have a certain fascination with women's breasts. Society feeds into this by putting the female chest on display everywhere from Hooters restaurants to nudie magazines to beer advertisements. But how do we explain men's obsession with these two mounds of fatty tissue? If you ask guys why they like breasts so much, you probably won't get too much insight other than "I don't know--I just do." So what do scientists have to say? Most theories, including a brand new one from the book The Chemistry Between Us, suggest that there is an evolutionary basis for it.
One of the earlier explanations, known as genital echo theory, proposes that female breasts only became a significant factor in attraction once human beings started walking upright.1 Before we started walking on two legs, the biggest source of visual excitement for men was the female buttocks. However, when we stood up, the buttocks was no longer as prominently displayed. As a result, the thought is that the breasts became bigger and more pendulous in order to mimic the visual appeal of the buttocks (think about it this way: cleavage bears a striking resemblence to the rear end, doesn't it?).
One of the newer theories is that men have evolved a preference for breasts because stimulating them enhances bonding with a female partner.2 The basic idea is that women find breast and nipple stimulation to be sexually pleasurable. In fact, some women find nipple stimulation so pleasurable that it can lead to orgasm in and of itself! In addition, such stimulation causes the release of oxytocin in the brain. Oxytocin is a hormone that facilitates bonding between humans. Research has shown that it plays a role in the bonding that occurs between mother and child during breastfeeding, as well as between romantic partners who have sexual contact. Some scientists believe that men have developed an attraction to breasts precisely because breast and nipple stimulation tap into this neurochemical bonding system that can bring couples closer.
Other theories certainly exist (e.g., breasts may also be desired because they indicate sexual maturity and fertility status), however none of them tell us definitively why heterosexual men tend to look at women's breasts like they are one of the seven wonders of the world. These theories are complicated by the fact that not all men are into breasts, and that there are big cross-cultural variations in terms of what men find attractive about the female body. Although scientists do not fully agree on a single explanation, there does seem to consensus that men's fascination with breasts has evolutionary roots.
Check more of Dr. Lehmiller's articles on his blog, The Psychology of Sex.
1Fisher, H. E. (1992). Anatomy of love. New York: Fawcett Columbine.
2Young, L., & Alexander, B. (2012). The chemistry between us: Love, sex, and the science of attraction. New York: Penguin.