Symmetrical Bodies Are More Beautiful to Humans

Ker Than
for National Geographic News
August 18, 2008
When considering a mate, people's assessment of physical beauty is mostly about symmetry, scientists say.

A new study finds that the more symmetrical a person's body is, the more appealing that person is to the opposite sex.

Previous research had shown that balanced facial features are considered more beautiful by observers, partially confirming notions put forth by the ancient Greeks that symmetry is an important ingredient in human judgments of beauty.

The new finding suggests that the same is true for body symmetry, and that symmetrical proportions could be signs of biological fitness.

"In animals with two sides that were designed by natural selection to be symmetrical, subtle departures from symmetry may reflect poor development or exposure to environmental or genetic stress," said study team member William Brown of Brunel University in the U.K.

"In many species these departures are related to poor health, lower survival, and fewer offspring."

The research is detailed in this week's issue of the journal Proceedings of the National Academy of Sciences.

Subtle Symmetry

Using a 3-D optical scanner similar to ones used in the medical and fashion industries, Brown and colleagues created detailed virtual models of the bodies of 77 adult human subjects and measured the models for degree of symmetry.

The researchers then asked a separate group of 87 volunteers to rate the attractiveness of bodies of the opposite sex based solely on visual appeal.

To remove any potential bias due to facial features or skin color, the heads of the virtual models were removed and the bodies were all tinted the same neutral shade.

Although differences in left-right symmetry are usually almost undetectable to the naked eye, both men and women reported symmetrical bodies to be more attractive.

The researchers also found that men with physical traits commonly associated with masculinity—such as greater height, broader shoulders, and smaller hip-to-waist ratios—tended to have more symmetrical bodies.

(Related: "Human Ancestors Needed Short Legs to Fight for Mates, Study Says" [March 19, 2007].)

Similarly, women who were more symmetrical tended to have more typical feminine traits, such as larger hips, longer and more slender legs, and larger breasts.

In an earlier study, Brown and his team found that people with more symmetrical bodies tend to be better dancers, which may indicate that dancing ability is a way of advertising other areas of physical fitness.

"It seems that because bodily asymmetries are too subtle to be seen with the naked eye, evolution has instead engineered more conspicuous signals and displays—such as broad shoulders, curvy waist lines, or smooth dance moves—to indicate mate quality," Brown said.

Objective Scans

John Manning, an evolutionary psychologist at the University of Lancashire, noted that in most cases, the differences between the left and right sides of a person's body are tiny—only about one to three percent.

Previous studies in which investigators used calipers to measure body symmetry were therefore highly susceptible to human error.

By contrast, using a 3-D scanner provides a more objective way of measuring body symmetries, said Manning, who was not involved in the research.

The new study also provides evidence of a strong relationship between body symmetry and sex-typical body features, he added.

"This means a woman who pairs with a man with a masculine body or a man who chooses a woman with a feminine body is likely to get a symmetric partner with all the associated fitness benefits," Manning said.

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