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Evolutionary Mysteries: Breasts, Part 2

Venus of Willendorf

For those of you who joined this class late, I’ve been speculating about possible answers to the evolutionary mystery, “Why do women, alone among all mammals, have prominent non-lactating breasts?” Time for hypothesis number three, another silly one:

3. Water wings? Elaine Morgan has long championed the bizarre idea that people evolved as “aquatic apes,” with breasts serving as flotation devices. After all, during World War II, sailors called their life-vests “Mae Wests.” Floating babies might have clung to their mother’s breasts as to water wings. And presumably men would have done the same (after all, even now, they do so whenever they can). Seriously, however, if breasts evolved as life preservers, then men ought to have evolved them, too. And also manatees. Moreover, the evidence is overwhelming that Homo sapiens didn’t evolve as semi-aquatic critters. Let’s return to reality.

4. Storage Sites? Maybe human breasts evolved as calorie storage sites, a kind of pantry that preceded refrigeration. If so, then the ample breasts of Earth Mother Goddesses would certainly have been preferred over those of today’s anorexic fashion models. There is a generally close correspondence between what people find sexually appealing and what ultimately leads to reproductive success, and so, it is not unlikely that our male ancestors preferred sexual partners whose well-upholstered bosoms suggested the ability to survive hard times, not to mention promising abundant nourishment for any eventual offspring.

But there are problems here as well. For one thing, breasts are unlikely to have evolved as storage sites; if calorie storage was evolution’s intent, it would have been far more efficient to use the hips, butt, or upper arms, where tissue could have been wrapped securely around bone instead of being left unsupported. (Any physically active woman will confirm that breasts are often a distinct liability.) Moreover, as already explained, fatty breast tissue doesn’t contribute to making milk and nonlactating breasts—whose prominence we are trying to explain—are composed almost entirely of fat.

On the other hand, breasts might nonetheless provide accurate information, indicating a woman’s ability to accumulate and store calories. Pleistocene era women who already had enough nutrition on board to readily expand their breasts—even if simply via fat deposition—would have been the most likely to stimulate males to provide yet more. This idea is especially compelling because it hints at a possible explanation for why prominent nonlactating breasts are so characteristic of human beings and not other mammals. The “explanation,” if valid, makes use of another trait that is especially characteristic of Homo sapiens: Our intellect and imagination. Thus, it seems almost certain that prehistoric men would have noticed that lactating women develop enlarged breasts, and not unlikely that human cognition would therefore have made an association between large-breastedness and effective milk production (even though such a correlation, as we have seen, turns out to be spurious).

And so, an early hominid female in a position to benefit from storing fat somewhere on her body might as well have done so via her breasts, in order to stimulate additional male investment … all the more so insofar as men would have been predisposed to prefer women with relatively prominent breasts.

This brings to mind what has been called the “banker’s paradox,” so named because banks are least favorably disposed toward those prospective borrowers who especially need a loan, because the more needy the would-be borrower, the more liable he is to be a poor credit risk. Conversely, they eagerly bestow funds upon the wealthy, who need it least. In short, those who have, and don’t need much more, get. Something along these lines may have induced evolution to exaggerate the breasts of early female hominids, because those thereby endowed would have profited from the increased self-interested largess of men, inclined to “lend” resources to a prospective mate deemed to be a good investment—whether or not they really are.

Next, we’ll look at some of my favorite hypotheses, which involve sexual selection and “honest signaling.” (Honest.)

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