Boobs

Perhaps tomorrow I’ll go back to writing about international trade imbalances, but what the heck, it’s Saturday. I should preface this whole entry by noting that you probably shouldn’t pay attention to what an economist has to say about evolutionary biology (unless that economist happens to be a biologist as well, which is certainly not the case with me). Nonetheless, it has been observed that, when the subject is boobs, people tend to pay attention no matter who’s talking.

Daniel Davies had an entry on Crooked Timber today entitled “Busty barmaids and other developments in science,” which reports the finding of a study (apparently a genuinely scholarly one, despite its subject matter) by the Cornell School of Hotel Administration: there is a linear relationship between the size of a barmaid’s breasts and the size of her tip. A linear relationship means that, no matter how big a barmaid’s breasts are, one with even bigger breasts will tend to get bigger tips. (I haven’t read the study, so I don’t know if they included a dummy variable for Shelley Long.) One might imagine that one of those BBW porn models with an alliterative pseudonym like “Henrietta Hugeones” would have an absolute advantage as a barmaid, even if her comparative advantage is in her field of choice. (Well, an absolute advantage as far as tipping goes; depending on the arrangement of the bar, she might be at a disadvantage in performing her service efficiently.)

Mr. Davies uses the study as an occasion to speculate on the topic of why men like big breasts (by which he apparently means, why they find women with big breasts sexually attractive). His theory seems to be that men have an unconscious facility that attempts to find good mothers for their children and that mistakenly “figures out” that big breasts are better for feeding infants. Then I suppose it unconsciously tells the men to pursue women with big breasts, even if the men aren’t consciously interested in having children. In order for this to work, the facility has to repeat its mistaken logic for each individual, because big breasts aren’t in fact better for feeding infants, so there is no selection pressure to prefer large breasts independently of that mistaken conclusion. It’s not a theory that I find compelling.

There is a related fact that one might also want to explain: the fact that women have distended breasts in the first place. It’s trivial to explain why lactating women have breasts, but in most species, the females don’t develop distended breasts until their first pregnancy. Among human beings, even virgins have boobs, which is a bit of an anomaly. You might say that women have breasts because men like them, but then you need an explanation for men’s preference that doesn’t get circular by depending on the fact that women have breasts. For example, one commenter suggests that men like big breasts because they are a sign of sexual maturity, which might be a fine explanation, except that it begs the question of why sexually mature virgins have breasts.

I would also note that the specific study discussed does not demonstrate that men find big breasts sexually attractive, only that men like to give gifts (in the form of larger than average tips) to women who have big breasts. That in itself is fairly easy to explain. Presumably in some proto-human species, big breasts (or any substantial breasts, for that matter) in a young woman were a reliable sign that she was pregnant or lactating. Giving gifts (which presumably would have taken the form of food) to pregnant and lactating women makes a lot of sense on the face of it (and also, as I will argue, had an evolutionary advantage). They are, after all, “eating for two,” and they presumably have a harder time foraging for their own food than most people do.

The following theory of breast evolution pulls it all together:

1. Among men who have surplus food (or surplus money to spend at bars), evolution favors the gene that predisposes them to give that food to women who look pregnant, because (in the evolutionary environment) such a woman had a disproportionate chance of carrying the man’s own offspring or that of a close relative, and because she needed food more (and would have a harder time getting food for herself) than a non-pregnant woman.
   
   
2. Among species that walk upright, so that their eyes don’t naturally look toward the belly, distended breasts are a particularly useful signal of pregnancy.
   
   
3. The genetic mutation causing virgins (and childless women in general) to have breasts was favored because it made them look pregnant, so that they would get goodies normally reserved for pregnant women. (Not consciously reserved, of course; it’s just that men like to give gifts to women who have this characteristic originally associated with pregnancy.)
   
   
4. A gene for sexual attraction to virgins with breasts (stronger the larger, and therefore more obvious, those breasts were) was favored because men who chose mates with a gene for virginal breasts would have daughters with virginal breasts, who would then get goodies normally reserved for pregnant women and be more likely to survive.
   
   
5. Then the whole sexual selection / positive feedback thing kicks in. There is an evolutionary advantage to a gene for attraction to a characteristic that others find attractive, since that gene makes your offspring more attractive, so that you’re more likely to have grandchildren. Then there is an evolutionary advantage to a gene that exaggerates such a characteristic in yourself because it makes you more attractive and therefore more likely to have children. Etc.