Assessing Fitness in Humans
An intriguing evolutionary hypothesis suggests that what men and women consider “beautiful” are traits that have evolved by sexual selection as proxies of fitness. In one set of studies, facial beauty was hypothesized to convey information about the genetic quality of the person to resist pathogens that lower health and shorten life expectancy. Pathogen resistance depends, among other factors, on the degree of immunocompetence. Many hormones that mediate the development of secondary sexual characters (androgens and estrogens) also lower immune activity. The wide jaw typical of men considered attractive by women is an example of a character controlled by the androgen testosterone. Such testosterone-dependent characters can signal the genetic quality of the bearer. Only highly fit individuals can cope with the handicap brought about by such characters, namely, a decrease in immunocompetence by high testosterone levels. Interestingly, extreme versions of features like jaw width are considered attractive by females and a signal of social dominance and health in several cultures (Grammer & Thornhill, 1994).
Female beauty is also based on some characters that signal the bearer’s fitness, as illustrated by studies of women’s waist-to-hip ratio (WHR). Men from different cultures rate as most attractive and sexy women who have a WHR of around 0.7, that is, the width of the waist is about 70% the width of the hip, independently of body weight. This preference holds even when men rate drawings of women varying in weight as well as in WHR (Singh, 1993). For
Figure 11.8 Men rated a series of drawings representing women which varied in terms of body weight and in terms of the waist-to-hip ratio (WHR). Attractiveness increased for all drawings as the WHR approached a value of 0.7. The effect of the WHR was evident even when the drawings were considered unattractive on the basis of body weight. The WHR can be appreciated in the photo of Venus, a paradigm of female beauty in the ancient world
Source: Singh, (1993); reproduced with permission from the American Psychological Association. Photo from Creative Commons, https://search.creativecommons.org, by Public Domain Photos Blog, licensed CC BY 2.0.
each weight category, the most attractive figures were the drawings representing a WHR of 0.7, even though underweight and overweight drawings were generally rated as less attractive than normal-weight ones (Figure 11.8). The WHR provides information about fitness. For example, a WHR close to 0.7 appears at puberty, is maintained until menopause, and is increased during pregnancy, all features providing information about the reproductive status of a woman. A WHR close to 0.7 also signals low risk for several forms of diabetes and cancer, gallbladder disease, hypertension, heart disease, stroke, and mortality, thus providing information on the woman’s general health status. Married women with WHRs approaching 0.7 have less difficulty to become pregnant and have their first baby at a younger age than women with higher WHRs. Therefore, a WHR close to 0.7 is a proxy for higher fertility and lower mortality, two variables that correlate with lifetime reproductive success.
The WHR depends on sex hormones that regulate fat deposition in the body. The difference between men and women lies not on the absolute amount of fat tissue, but on its distribution. Before puberty, both boys and girls have a WHR close to 0.9. At puberty, estrogen (present predominantly in women) favors the deposition of fat tissue in the glute-ofemoral region, thus increasing hip width and reducing the WHR. By contrast, testosterone (present predominantly in men) favors fat deposition in the abdominal region, keeping the waist width relatively high and increasing the WHR. As a result, adult WHRs show a distribution with practically no overlap: 0.67 to 0.80 for healthy women and 0.85 to 0.95 for healthy men.
