Are Busty Women More Promiscuous?

The stereotype is pervasive, but the scientific evidence is weak.

There’s no question that most men find large breasts to be sexually appealing. In field studies, psychologists find that busty women are approached more frequently in bars and nightclubs, get rides more easily as hitchhikers, and receive higher tips as waitresses compared to women with smaller breasts. And yet, the question of why women have protruding breasts is itself an evolutionary conundrum. Breasts, of course, are for producing milk to feed babies, and yet the females of other mammal species rarely sport such ponderous protuberances, even when they’re lactating for an entire litter. Furthermore, studies show that, even among humans, breast size isn’t correlated with either the quantity or quality of milk that mothers produce. None of these facts, then, explains why women have protruding breasts, or why men find them so sexually enticing.

Plenty of evolutionary theories have been proposed in an attempt to explain this conundrum. One theory is that large breasts are an honest signal of health: That is, only women in exceptionally good health can build and support these heavy appendages. Another theory is that they signal fertility, in that the fat stored within them demonstrates they have ample biological resources for making and feeding babies. And a third theory is that they evolved to signal a willingness to engage in casual sex as opposed to pair-bonding. To see whether they could find evidence to support any of these theories, Polish psychologist Krzysztof Koscinski and colleagues recruited 163 young women who were willing to undergo a battery of physiological and psychological assessments. The goal was to see whether breast size was correlated with known markers of health and fertility or with self-reported attitudes about sexuality, particularly openness to casual sex. The first set of measures looked at breast size and body type. As expected, breast size was uncorrelated with height, but it was correlated with weight and body mass index. In other words, heavier women tend to have larger breasts, a finding that was unsurprising. The second set of measures considered the hypothesis that breast size is a signal of health. The researchers took a medical history of respiratory and digestive infections for each woman as an indicator of susceptibility to disease. They also measured body symmetry, a known marker of developmental stability. That is, healthy children tend to grow into adults with symmetrical bodies, while unhealthy children tend to display bodily imbalances when they grow up

The results were mixed. The large-breasted women had more respiratory infections, but they had the same number of digestive infections as smaller-breasted women. However, they did show more body symmetry than other women, which may suggest something about the need for a healthy childhood in order to have the bodily resources to grow large breasts after puberty. The third set of measures tested the notion that large breasts signal fertility. In particular, the researchers tested for the levels of two hormones in each woman’s saliva, estradiol and testosterone. A high level of estradiol in women is a known indicator of fertility, while a high level of testosterone often signals problems with pregnancy and childbirth. The results showed that breast size wasn’t correlated with levels of either of these two hormones, thus suggesting that large breasts are not, in fact, signals of fertility. The fourth set of measures assessed the women’s level of sociosexuality or openness to casual sex. This time, the participants responded to a questionnaire about their attitudes and behaviors regarding short-term sexual encounters with multiple partners. Again, the researchers found no evidence that busty women are more interested in casual sex than their less well-endowed counterparts. In short, the study failed to find evidence to support any of the three evolutionary theories about why women have breasts. The researchers admit that their sample size was fairly small, and likewise, they may not have selected the right correlates of health and fertility. Furthermore, it’s possible that the women in this study didn’t honestly report on their sexual attitudes and behaviors. However, the researchers employed a standard test of sociosexuality that has been used successfully by other psychologists. Although the researchers found no evidence that busty women are more promiscuous, they were also curious about the social nature of this stereotype. In particular, the researchers asked whether only men entertain this belief about large-breasted women, or if women also hold this notion.

To explore this question, the researchers started with a photograph of a topless young woman with average-sized breasts. Using body morphing software, they either increased or decreased her breast size, thus creating three versions of an otherwise identical woman with her bust large, medium, or small. They then asked over 500 men and women to rate the woman in each of the three images on a range of traits. Perhaps the most interesting finding of all was that men and women largely agreed in their assessments of the woman with large, medium, or small breasts. Both men and women rated the woman with either large or medium breasts as equally attractive and suitable as a wife, more so than the small-breasted woman.

However, the respondents rated the large-breasted version as most sexually attractive and also more open to casual sex than when the woman’s breasts were medium or small. They also believed the large-breasted woman to be less faithful, less intelligent, and less diligent than either the medium or small version. Additionally, they displayed attitudes in line with the evolutionary hypotheses stated above, in that they rated the woman’s ability to bear children and produce milk highest in the large-breasted version, followed by medium and small. While the researchers found no evidence that busty women are more promiscuous than their medium or small-breasted counterparts, they did find widespread belief in this stereotype among both men and women. In conclusion, they warn readers not to judge the sexual attitudes of women on the basis of physical appearance. More generally speaking, it’s always a wise choice to assess people’s attitudes on the basis of their behavior and not their body type.