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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