Why Do Women Have Breasts, Anyway?
9:45 am, May 11th | by Florence Williams
Clearly, many anthropologists love breasts. In textbook illustrations and museum dioramas, they always seem to depict the latest evolutionary “missing links” with breasts, despite zero fossil evidence for this. Ardi? Lucy? Breasts and more breasts. Even Mrs. Bigfoot is often drawn with a comely pair. We all know men like Morris; there are lots and lots of them. But there are also some leg men out there, like my husband, God bless him. In any case, the science of sexual attraction has been marked by fierce debate and bald accusations of cultural bias that continue to this day.
Try telling some feminist anthropologists that breasts exist because of men, and you might get whacked in the head by a rubber Australopithecus pelvis. Elaine Morgan, a Welsh writer, wrote an entire, rather delicious book refuting Morris and his ilk, called The Descent of Woman. In it, she thoroughly debunked the notion that the needs of the male drove every clever anatomical adaptation in human ancestors, including breasts. “I find the whole yarn pretty incredible,” she wrote. “Desmond Morris, pondering on the shape of a woman’s breasts, instantly deduces that they evolved because her mate became a Mighty Hunter, and defends this preposterous proposition with the greatest ingenuity. There’s something about the Tarzan figure which has them all mesmerized.”
Frances Mascia-Lees, a Rutgers University anthropologist, told me she thinks the scholarship over the past fifty years on breasts and attraction has been a colossal waste of time. “When you talk about the old guys, the same arguments are still being made. They will not die under any circumstance. But when it comes to finding a mate and having children, breast size does not matter, even though many advertisers and plastic surgeons might love us all to think so,” she said.
She pointed to a number of holes in the breasts-as-sex-signals theory of origin. If big, firm breasts tell a man that a woman is fertile and ready for sex, then why would her breasts be biggest and firmest when she’s already pregnant or lactating? Why is there such huge variation in human breast size and shape, and why are so many women with tiny breasts spectacularly successful at nursing, childbirth, and child-rearing?
Although I hate to admit it, I couldn’t help wondering if Mascia-Lees herself has tiny breasts and if that had influenced her contrarian worldview. So I asked her, and it turns out she has the opposite problem. She’s a 36DD. When she entered graduate school in 1981, her department consisted of fifteen men and one woman. The American obsession with breasts was annoyingly evident. “Having big breasts meant you were highly sexualized by men,” she said. “It was a prickly issue for me trying to be taken seriously as an intellectual.” At the time, the Mighty Hunter theory was everywhere. He drove the evolution of the bigger brain, speech, social behavior, bipedalism, the use of tools, and so on. It rankled. It got her thinking. In a sweet-vengeance counter-scenario, Mascia-Lees and others instead argue that it’s just as likely the female drove these developments, through lactation and the unique demands of the human infant. Just suppose for a moment, gentlemen of the academy, that breasts evolved because she needed them, not because her club-wielding cave man did.
Mascia-Lees argues that breasts evolved through natural selection, not sexual selection. It seems perfectly reasonable, if not more reasonable, to suppose there was something about having breasts that increased the fitness of the woman and her offspring in what Darwin plaintively calls the “struggle for existence.” Male interest, if it even exists universally, was secondary. She posits that breasts helped increase a woman’s fat reserves, even if just by a few percentage points. In the poor or unpredictable environment of our early evolution (such as the open plains with their greatly fluctuating temperatures), those extra fat depots could have made the difference in being able to sustain pregnancy and lactation. Humans need to store more fat than other primates because they don’t have fur to keep them warm. On top of that, pregnant humans need to mobilize more fat to keep pace with their pudgy babies, whose big brains need specialized stores of long-chain fatty acids. Consequently, women’s bodies are designed in such a way that they don’t even ovulate unless a body-fat threshold has been crossed. On average, reproductive-age women store twice the fat that men do.
But why store fat in the breasts and not, say, the elbow? Mascia-Lees has a good explanation for this. Fat and cholesterol make estrogen. Mammary glands are filled with estrogen-sensitive cells. We have more estrogen than other primates simply because we’re relatively fatter. Here’s the sequence: we needed to be fatter at puberty and beyond to produce human infants; our fat made estrogen, and estrogen made our breasts grow because the tissues there are so attuned to it.
In Mascia-Lees’s account, breasts are merely “by-products of fat deposition.” She admitted her theory is not nearly as testable, or as sexy, as that of the Morris crowd. But that’s the point. “I’ve tried to show that my assumptions are more firmly grounded,” she said, “and not just the same cultural assumptions we have now projected back into evolutionary history.”