Symmetry the key to sexual appeal

Scientists say when it comes to searching for a partner, the attraction of a potential mate is all about symmetry.

They say how symmetrical a person's body appears, the more attractive that person is to the opposite sex.

The idea that perfectly balanced features represent beauty is not a novel one, as far back as ancient Grecian times symmetry was regarded as an important ingredient in human judgments of beauty.

More recently beauties Greta Garbo and Marlena Dietrich were both considered to be remarkable for their perfectly symmetrical facial features and the same might be said of some of today's top models.

In new research from scientists at Brunel University in London, it is suggested that the same is true for body symmetry, and that symmetrical proportions could be signs of biological fitness.

Study leader Dr. William Brown says 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.

He says in many species these departures are related to poor health, lower survival, and fewer offspring.

The researchers used a 3-D optical scanner, not dissimilar to ones used in the medical profession, to create detailed virtual models of the bodies of 77 adult human subjects which were measured for degrees of symmetry.

Brown and his colleagues then asked another group of 87 volunteers to rate the attractiveness of the bodies of the opposite sex based solely on visual appeal.

In order 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.

Even though differences in left-right symmetry are as a rule almost undetectable to the naked eye, both men and women reported symmetrical bodies to be more attractive.

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

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 earlier research the Brunel team had found that people with more symmetrical bodies tended to be better dancers, which possibly suggests that dancing ability is a way of drawing attention to other areas of physical fitness.

Brown says it appears 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.

Experts say in most cases, the differences between the left and right sides of a person's body are very small and the use of the 3-D scanner provides a more objective way of measuring body symmetries.

They say the research provides evidence of a strong relationship between body symmetry and sex-typical body features, which means a woman who mates 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.

Dr Brown says the 3D body scanner accurately extracts hundreds of measurements of the human body, including volume, in six seconds and removes a potential source of measurement error, the human experimenter.

The research is published in the current issue of the journal Proceedings of the National Academy of Sciences.