Both men and women find members of the opposite sex more attractive if they have symmetrical bodies -- not just symmetrical faces -- new research says.

Researchers from Brunel University in the United Kingdom found that study subjects deemed the most symmetrical body type to be 63 per cent more attractive compared to the most asymmetrical body type.

Previous research has shown that most people find a symmetrical face to be more beautiful than an asymmetrical face.

Researchers believe humans are more attracted to symmetrical faces and bodies because they are signs of a more desirable mate. Humans may perceive asymmetrical features to be a sign of weakness or disease, which may make procreation difficult.

"Symmetry reflects good development," lead study author, William M. Brown, told in an email interview.

"In animals with two sides that were designed by natural selection to be symmetrical, subtle departures (one to three per cent of trait size) from perfect symmetry may reflect poor development or exposure to stress (environmental and/or genetic). In many species the degree of departure from perfect symmetry is related to poor health, lower survival and fewer offspring."

The findings are published in the journal Proceedings of the National Academy of Sciences.
Brown and colleagues used a 3-D optical scanner to create detailed, 360 degree images of the body shapes of 77 people. The images were a neutral colour and did not include heads, so subjects would not be influenced by factors such as facial characteristics.

The team then asked 87 people to rate bodies of the opposite sex for attractiveness.

They also asked the study subjects to evaluate the body types for so-called "body masculinity," which includes male characteristics such as greater height, wider shoulders and smaller breasts.
The subjects found symmetric men with high body masculinity and symmetric women with low body masculinity the most attractive.

Brown said this research leads to two avenues of study. First of all, researchers are investigating how body masculinity and femininity might influence body movement.

He said that humans, like other animals, may also choose mates based on physical movements, ranging from dancing to changing facial expressions, that they find attractive.

As well, Brown would like to investigate "if symmetrical people have more high quality offspring than asymmetrical people."

Brown pointed to American data that suggested symmetrical newborns were physically and mentally healthier compared to their more asymmetrical counterparts. However, this data omitted information about the symmetry of the babies' parents.


Fluctuating asymmetry and preferences for sex-typical bodily characteristics
William M. Brown, Michael E. Price, Jinsheng Kang, Nicholas Pound, Yue Zhao, and Hui Yu
Body size and shape seem to have been sexually selected in a variety of species, including humans, but little is known about what attractive bodies signal about underlying genotypic or phenotypic quality.

A widely used indicator of phenotypic quality in evolutionary analyses is degree of symmetry (i.e., fluctuating asymmetry, FA) because it is a marker of developmental stability, which is defined as an organism's ability to develop toward an adaptive end-point despite perturbations during its ontogeny.

Here we sought to establish whether attractive bodies signal low FA to observers, and, if so, which aspects of attractive bodies are most predictive of lower FA. We used a 3D optical body scanner to measure FA and to isolate size and shape characteristics in a sample of 77 individuals (40 males and 37 females). From the 3D body scan data, 360° videos were created that separated body shape from other aspects of visual appearance (e.g., skin color and facial features).

These videos then were presented to 87 evaluators for attractiveness ratings. We found strong negative correlations between FA and bodily attractiveness in both sexes. Further, sextypical body size and shape characteristics were rated as attractive and correlated negatively with FA. Finally, geometric morphometric analysis of joint configurations revealed that sex-typical joint configurations were associated with both perceived attractiveness and lower FA for male but not for female bodies.

In sum, body size and shape seem to show evidence of sexual selection and indicate important information about the phenotypic quality of individuals.