The Science of Sex: Computing Beauty Part Two: Balanced Beauty

“What immortal hand or eye / Could frame thy fearful symmetry?” Thus mused poet William Blake about one of nature’s most beautiful creations, the tiger. The beauty of humans, like that of tigers and many other animals, is closely tied to the bilateral symmetry of their bodies and faces. Small deviations from perfect anatomical symmetry can have enormous consequences for the way people are perceived and treated, and hence for their success and happiness in life.

Several studies have shown that people with highly symmetric faces and bodies are seen as more attractive than people with asymmetric features. A particularly nice demonstration of this comes from a 1999 study by psychologist Linda Mealey and her colleagues at the Universities of Queensland and Adelaide, Australia. (Mealey is now at the College of St. Benedict in St. Joseph, Minnesota.)

Mealey obtained photographs of thirty-four pairs of monozygotic or “identical” twins and asked sixty-three male and female college students to judge which twin out of each pair was the more attractive.

Although monozygotic twins

share the same genetic endowment, the vicissitudes of their individual developments ensure that they end up looking slightly different from each other. In the example shown here, most students rated the twin on the right (B) as more attractive than the one on the left (A).

Mealey then used a computer to make two composites of each face. In each composite, one half of the image — say the left — was the real image of one side of the person’s face, while the other half was a mirror-reversed version of that same half-image. Call this the “double-left” image. The other composite was the “double-right” image.

Obviously, the more symmetric the original face, the more similar the double-left and double-right composites of that face would look.

Mealey asked another set of seventy-five students to look at these composites and say whether the composites for twin one or for twin two were more alike.

This would determine which twin’s face was perceived to be more symmetric. Consistently, the twin who was judged as more symmetric was also judged as more attractive, even though the two judgments were made by different people. In the examples shown here, the lower pair of images (B), made from the “more attractive” twin, are more similar to each other than are the upper pair of images, made from the “less attractive” twin (A).

Why is symmetry attractive? In terms of evolutionary psychology, the answer is something like this: both sides of a person’s body develop under the influence of the same set of genes, so the left and right sides can be thought of as two independent “read-outs” of a person’s genetic instructions. If the two sides are very similar, that suggests that both sides developed in accordance with the person’s genetic “design specifications” and therefore, that his or her genes were good ones or that they did not encounter any adverse environmental factors (such as disease) during development. If the two sides are dissimilar, that suggests that the person’s genetic instructions were relatively ineffective or that some adverse environmental factors interfered with development, leading to asymmetry. Thus, one would do better to mate with a symmetric person, and nature has endowed us with the desire to do so. Not just humans, but also mammals and birds look for symmetry in their mates. When researchers adjust the display feathers of male birds to make them less symmetric, female birds reject their courtship.

Numerous studies have reported on the positive attributes of highly symmetric people. They are less likely to have been born prematurely or to suffer from chromosomal defects; they suffer less from a variety of physical and mental diseases, including schizophrenia; they report having experienced less emotional and physiological stress; they are more physically robust, socially dominant and intelligent; if male, they have sex earlier in life, have more total sex partners and (according to interviews with their partners) satisfy their partners better. Some of these positive attributes may simply be consequences of the attractiveness of symmetric people, but most are not. Thus, the degree of symmetry in a person’s face or body offers a valuable clue as to whether he or she would be a good person to mate with. No wonder we are attuned to recognizing the subtle differences between highly symmetric and less symmetric people and to finding the symmetric man or woman more attractive.

Curiously, we are capable of assessing people’s symmetry by other means than the direct visual perception of left-right similarity. For example, people prefer the faces of highly symmetric people, even when they can see only one side of each face and therefore cannot assess left-right symmetry directly. Therefore there must be a correlation between symmetry and other aspects of attractive facial appearance — such as clear skin, perhaps.

In one remarkable study, psychologist Anja Rikowski of the Ludwig Boltzmann Institute in Vienna provided preliminary evidence that people can smell other people’s symmetry. Rikowski reported that men find the body odor of symmetric women sexier than that of asymmetric women, even when they have not seen the women themselves. (The men sniffed T-shirts the women had worn, rather than sniffing the women directly.) This result did not reach statistic significance, and it needs to be confirmed. Still, it fits with the notion that a variety of traits affecting the attractiveness of a partner go along with his or her degree of symmetry.

So, if you’re looking for greater success in the romantic department, plastic surgery to make you more symmetric might help. But don’t invest too much in it — your prospective partners may still be able to sniff out your true biological worth.

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