Shown drawings of six different women, three hourglass- shaped (U7 - O7), and three thick-waisted (U9 - O9), one man from Yomybato said the slim hourglass-shaped woman (U7) was "skinny in the waist," and "had diarrhea." The heavier hourglass woman (O7) was "almost better," but O9, a thick-waisted woman who is overweight by western standards, ranked as most appealing.

She (O9) was "healthy," as compared to the skinny, thick-waisted woman (U9), who the man said was "pale" and "almost dead."

Men from from the same region, but outside Manu Park, were also surveyed.

Those with exposure to western influence preferred the hourglass figures (U7 - O7), reinforcing Yu and Shepard’s claim that preference for body type is socially influenced.

"Physical features are involved in mate choice, and natural selection has probably shaped those preferences," according to Yu and Shepard’s study. But these natural tendencies are repressed in societies where kinship rules or social status may overrule physical preferences.

With the daily exposure to strangers in today’s society, natural selection by beauty may be becoming more important again, according to the biologists.

"You’re forced to judge people by their faces," Yu says, describing how our daily interaction with strangers may affect the importance of beauty. "Maybe our obsession with physical beauty is based on our environment. You see more strangers in one day in New York City than people in Matsigenka see in their whole lives."