Monday, March 17, 2014

Waist not, want not?

In the previous post, I waxed on about the body shapes of the gods and goddesses at the Hindu temple in Madurai, India and wondered how the ideas of sexual selection (when features evolve because they help attract a mate) proposed by scientists such as Charles Darwin might apply to body shape in humans.

gets embarrassed discussing sexual selection
photo: DailyMail
Skin color and facial features, such as eye shape or nose size, affect people's attractiveness, but they don't give information about their reproductive capability the way body size and shape do. A woman's waist size is an easily-measured indicator of levels of the sex hormone estrogen for any man wanting to size up her reproductive potential (and pregnancy status).

Remember, we are all here because our distant ancestors were biologically fit enough to survive long enough to find a mate, successfully find that mate, and have kids healthy enough to do the same, so reproductive capability is no laughing matter.

The waist-to-hip ratio

Measure your waist, divide that number by the measurement around your hips, and you get your waist-to-hip ratio (which we'll call WHR for short). Go ahead, you don't have to tell us.

Hindu goddesses combine divine power
with unattainable killer curves
Women's higher levels of the hormone estrogen produce fatty deposits in their butts, hips, and upper thighs, but not their waists, so women's WHRs are typically lower than men's. This difference between men and women plays a big role in their respective ideas on attractiveness of the opposite sex.

For example, winners of the Miss America competition between the 1920s and 1980s, as well as many movie stars and Playboy bunnies have WHRs between 0.68 and 0.72. The corresponding WHRs for studly guys usually resides around 1.0, i.e. men's waist and hips are about the same circumference.

WHR not only is an identifying difference between men and women, it is also linked to reproductive capacity and reproductive age (WHR rises in women after menopause -- something to look forward to, right?)

Male university students in the U.S. tend to prefer slender, large-breasted women with small waists for both short- and long-term relationships and are considered more attractive, feminine looking, and healthy. I know, shocking. The researchers studying these preferences suggest that, to these young men from an affluent country, figures that were overweight or had a relatively larger waist implied an older woman and one with lower sex hormones.

Biological or societal?

Matsigenka men preferred the "overweight"
figures and those with relatively thicker waists
image from Yu and Shepard (Nature, 1998)
Nevertheless, social pressure shapes each of our views of what is attractive, whether or not it is healthy. Few cultures escape the extensive reach of the western media, but several studies have quantified and analyzed opinions of female body shapes among men of isolated hunter-gather groups who lack access to western media that might influence their opinions on female attractiveness.

A 1998 scientific paper that compared the views of female attractiveness and health by men of the Matsigenka tribe from the forests of southeastern Peru. These men judged the relative beauty and predicted health of images of women with several body types: thin, average, heavy, with waist-to-hip ratios of 0.9 and 0.7 (similar to those used in studies elsewhere).

While a small waist-to-hip ratio is considered a beauty standard, it was not favored by Matstigenka men in these groups, who preferred heavier women and those with larger (0.9) WHRs to thinner ones and those with a smaller (0.7) WHRs.

In fact, unlike other studies of young men from the US, England, and Germany, the Matsigenka men thought that thin female images and those with smaller waists perhaps had been sick and had lost weight, and images in the "overweight" category and those with relatively larger waists were healthier and more attractive.

Even more interesting were the reactions of a separate Matsigenka group that lived outside the forest but with very limited influence from western media: while these groups also preferred the "overweight" body images and agreed that higher WHRs were healthier, they thought the figures with smaller WHRs were more attractive.

The preferences of a third, more westernized, group living in the same area resembled those of western males: they preferred a "normal" body images with smaller WHRs - perhaps an example of how repeated exposure to cultural stereotypes influences people's views of some of our most basic feelings and actions?

an Amerindian beauty/heritage contest - note the waist-to-hip ratios
photo: Kaieteur News

Like the Matsigenkas, men of the Hadza tribe of Tanzania surveyed with similar images also preferred heavier women and those with a higher WHR than did men from the US.

However, in a follow-up study comparing U.S. and Hadza men's preferences for women using both front and side images of women, the Hadza guys selected the figures with more protruding butts, which elevated the hip measurement relative to their waist, creating a low waist-to-hip ratio.

So, is the desirability for women with a low waist-to-hip ratio among much of the world a search for high fertility, and therefore biologically based?  Or does society's pervasive influence, in the form of tradition or media, affect each individual's preferences in the search for a mate?

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