The Key to Female Attractiveness?

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What makes women attractive? It's a simple question, but it has been a topic of debate among evolutionary psychologists and anthropologists for decades.

One one side, there are scholars who argue that female fertility and perceived health are the key determinants of judgments of physical attractiveness.

They point to evidence showing that a small waist-to-hip ratio (WHR) and a low body mass index (BMI)—two traits that are generally preferred by men—are more likely to be found in women with enhanced health and fertility.

On the other side, some scientists believe nubility—that is, perceived youthfulness—is the key ingredient.

Scholars in this camp cite evidence that men are most attracted to women who have only recently entered physical and sexual maturity (and who have not yet been pregnant), as these are clear signs of high reproductive potential.

In many ways, these two hypotheses are at odds with each other. In well-nourished populations, nubility peaks around ages 15-19, while maximum fertility is not reached until the mid- to late-20's.

Moreover, the years when nubility is at its highest tend to be a period of relatively low fertility, due to decreased ovulation frequency. And, despite the health advantages conferred to infants by youthful moms, there is data to suggest that first pregnancies have a lower success rate than subsequent pregnancies.

Which account is correct? Or, evolutionarily speaking, which age group has the higher reproductive potential (i.e., the best chance of producing viable offspring)?

While scientific consensus has not yet been reached, a new study published in the journal Evolution and Human Behavior offers evidence in favor of the nubility hypothesis.

To arrive at this conclusion, researchers at the University of California Santa Barbara analyzed data from over 12,000 female participants under the age of 50 who took part in the National Health Examination Survey (NHANES III) between 1988 and 1994.

The researchers hypothesized that smaller waist-to-hip ratios and BMIs—traits typically associated with health and fertility—would actually be at their most desirable levels in nubile women, not during peak fertility. They also predicted that nubile women would have higher levels of omega-3 fatty acids—nutrients that play a critical role in infant brain development.

This is exactly what they found. Waist-to-hip ratios, BMIs, and thigh-to hip ratios were all at their most desirable levels when nubility was at its highest. Once women reach peak fertility, these ratios become more aligned with what is found in the overall female population.

The researchers write, "Our analysis suggests that a low WHR is a strong indicator of nubility because it reaches a clear minimum in the age range when skeletal growth was completed [...]. The waist/thigh ratio (though not frequently used in studies of attractiveness) shows a similar pattern. Moreover, both BMI and waist/stature ratios were also significantly lower in the nubile age group than in older women."

Furthermore, omega-3 fatty acids appear to be most abundant in nubile women. The authors state, "In our current sample, both lower waist/stature and lower waist/thigh ratios were associated with a higher percentage of DHA in plasma fatty acids. Our findings are concordant with the results of previous studies showing that a lower BMI and WHR indicate higher levels of omaga-3 fatty acids in the blood."