Jokes about bréasts, and men looking at bréasts, are such a comedy staple they've become a kind of go-to cliché. How many times have we seen a man talking to a curvaceous woman only to have her point to her own eyes and say "Hey, buddy, up here!"?
It's funny -- or, at least, it was funny the first dozen times we saw it -- because it's true. The male eye does have a way of drifting south. But why? Why are heteroséxual men so fascinated by women's bréasts that we sometimes act as if the bréasts are the seat of the soul?
Biologically speaking, this human male bréast obsession is pretty weird. Men are the only male mammals fascinated by bréasts in a séxual context. Women are the only female mammals whose bréasts become enlarged at puberty, independent of pregnancy. We are also the only species in which males caress, massage and even orally stimulate the female bréasts during foréplay and séx.
Women do seem to enjoy the attention, at least at the right moments. When Roy Levin, of the University of Sheffield, and Cindy Meston, of the University of Texas, polled 301 people -- including 153 women -- they found that stimulating the bréasts or nipplés enhanced séxual arou sal in about 82 percent of the women. Nearly 60 percent explicitly asked to have their nipplés touched.
Men are generally pretty happy to oblige. As the success of Hooters, "men's" magazines, a kajillion websites, and about 10,000 years of art tell us, men are extremely drawn to bréasts, and not because boys learn on the playground that bréasts are something that they should be interested in. It's biological and deeply engrained in our brain. In fact, research indicates that when we're confronted with bréasts, or even bréast-related stimuli, like bras, we'll start making bad decisions (and not just to eat at Hooters).
For example, in one study, men were offered money payouts. They could have a few Euros right away, or, if they agreed to wait a few days, more Euros later. In this version of a classic "delayed gratification" (also called intertemporal choice by behavioral economists) experiment, some men watched videos of pastoral scenes while others watched videos of attractive women with lots of skin exposed running in slo-mo, "Baywatch" style. The men who watched the women's bréasts doing what women's bréasts do opted for the smaller-sooner payouts significantly more often then men who watched the pastoral scene.
This likely indicates that parts of their brains associated with "reward," the pleasure centers, and the sites of goal-directed motivation, were shouting down the reasoning centers of their brains, primarily the pre-frontal cortex. Neurochemicals were activating those reward and motivational circuits to drive men toward taking the short money.
So bréasts are mighty tempting. But what purpose could this possibly serve?
Some evolutionary biologists have suggested that full bréasts store needed fat, which, in turn, signals to a man that a woman is in good health and therefore a top-notch prospect to bear and raise children. But men aren't known for being particularly choosy about séx partners. After all, spérm is cheap. Since we don't get pregnant, and bear children, it doesn't cost us much to spread it around. If the main goal of séx -- evolutionarily speaking -- is to pass along one's genes, it would make more sense to have séx with as many women as possible, regardless of whether or not they looked like last month's Playmate.
Another hypothesis is based on the idea that most primates have séx with the male entering from behind. This may explain why some female monkeys display elaborate rear-end advertising. In humans, goes the argument, bréasts became larger to mimic the contours of a woman's rear.
We think both of these explanations are bunk! Rather, there's only one neurological explanation, and it has to do with brain mechanisms that promote the powerful bond of a mother to her infant.
When a woman gives birth, her newborn will engage in some pretty elaborate manipulations of its mother's bréasts. This stimulation sends signals along nerves and into the brain. There, the signals trigger the release of a neurochemical called oxytocin from the brain's hypothalamus. This oxytocin release eventually stimulates smooth muscles in a woman's breasts to eject milk, making it available to her nursing baby.
But oxytocin release has other effects, too. When released at the baby's instigation, the attention of the mother focuses on her baby. The infant becomes the most important thing in the world. Oxytocin, acting in concert with dopamine, also helps imprint the newborn's face, smell and sounds in the mother's reward circuitry, making nursing and nurturing a feel-good experience, motivating her to keep doing it and forging the mother-infant bond. This bond is not only the most beautiful of all social bonds, it can also be the most enduring, lasting a lifetime.
Another human oddity is that we're among the very rare animals that have séx face-to-face, looking into each other's eyes. We believe this quirk of human sexuality has evolved to exploit the ancient mother-infant bonding brain circuitry as a way to help form bonds between lovers.
When a partner touches, massagés or nibblés a woman's bréasts, it sparks the same series of brain events as nursing. Oxytocin focuses the brain's attention to the partner's face, smell, and voice. The combination of oxytocin release from bréast stimulation, and the surge of dopamine from the excitement of foreplay and face-to-face séx, help create an association of the lover's face and eyes with the pleasurable feelings, building a bond in the women's brain.
So joke all you want, but our fascination with your bréasts, far from being creepy, is an unconscious evolutionary drive prompting us to activate powerful bonding circuits that help create a loving, nurturing bond.
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