AsianScientist (Sep. 4, 2015) – Scientists have found that body fatness has a direct impact on female attractiveness ratings among men and women, showing that the lower the body mass index (BMI), the higher the attractiveness ratings. Their study, published in PeerJ, paves a way for us to better understand the genetic basis for obesity and traits that play key roles in natural selection.
Evaluation of attractiveness is a key survival instinct that goes beyond butterflies in the stomach. In particular, female attractiveness stands out because a female’s health and fertility has direct consequences on bearing and raising children.
In former times when famine was common, fatter individuals may have a higher chance of survival compared to thinner individuals, putting fatter individuals on an evolutionary advantage. Yet in current times where food is mostly abundant, obesity in these same individuals ensue. This reasoning forms the basis for ‘thrifty gene hypothesis,’ which attempts to explain why the predisposition to diabetes has persisted at the population level.
“We wanted a way to test [the thrifty gene hypothesis]. Based on this hypothesis, we predicted that fatness would be a secondary sexual trait that people would see fat people as attractive,” explained Professor John Speakman, corresponding author of this study, from University of Aberdeen and Chinese Academy of Sciences.
The authors first formulated a mathematical model that takes into account female mortality with BMI. It predicted that the optimal range of BMI that one may find attractive to be between 22.8 to 24.8. They went on to show various body shapes and sizes to three different cohorts of participants: Asian, Africans and Caucasians and asked them to rate the images’ attractiveness.
Contrary to their initial mathematical model, they found that the optimal BMI where all three cohorts of people find attractive is between 18.4 to 21.4 (that is about 9 to 16.5 kg difference in body weight from the predicted values).
When the researchers took into account the age factor in the model prediction, the optimal BMI went down to between 17 to 20, close to the experimental data obtained. This means that people use body fatness as a proxy for age. Indeed, the author found a strong correlation between BMI and predicted age by the assessor. As age is an important factor in health and fertility, it cannot be disregarded in the prediction model.
Their work suggests that the thrifty gene hypothesis may not contribute towards the global obesity pandemic as body fatness is not deemed attractive in the population. Hence is it not a trait that is actively selected by the crowds.
“People seem to prefer much thinner individuals than the model predicted. The findings do not support the idea that famine was a strong selective force for body fatness,” Speakman told Asian Scientist Magazine.
The article can be found at: Wang et al. (2015) The Relationship of Female Physical Attractiveness to Body Fatness.
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Copyright: Asian Scientist Magazine; Photo: University of Aberdeen.
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