Facial symmetry and gender perception

Beauty is an advert for good genes, reports The Daily Telegraph today. It says that “research conducted across cultures and species”, has found that not only are symmetrical faces regarded as being more attractive, but that they also may indicate good genes, health and long life.

The newspaper story is based on research which investigated whether facial symmetry is linked to how feminine or masculine a face is considered to be. However, this research has not investigated or suggested that increased facial symmetry, or “beauty” as the Telegraph describes it, is linked to better genes and that asymmetry is linked to less favourable genes. These are evolutionary theories that have been previously been suggested, mainly in the context of animal mating patterns. The first line of the news article that “beautiful people are healthier and live longer” may or may not be the case, but as this research did not investigate this, it cannot add any evidence either way.

Where did the story come from?

Anthony Little of the University of Stirling’s School of Psychology and colleagues from the universities of Aberdeen, Oxford and St Andrews, McMaster University in Canada, Harvard University and Florida State University, in America, carried out this research. Individual researchers received a Royal Society University Research Fellowship, a National Science Foundation grant and support from Unilever research. The study was published in the peer-reviewed online scientific publication: PLoS ONE .

What kind of scientific study was this?

This was an experimental study which looked at the evolutionary theory that more desirable traits are passed on to future generations because there is a preference for the selection of an individual with that trait as a mate. For example, a male bird with long tail feathers is observed as being more “attractive” and therefore the females would be more likely to mate with him, thus passing on the trait of longer tail feathers.

Across many species, facial symmetry and sexual dimorphism (a man or woman being seen to have more classically masculine or feminine features, respectively) are suggested to be indicators of a good "mate” who will have good genes which can be inherited by the next generation. In humans, having more masculine features is also thought to be linked to higher testosterone levels and more feminine features related to higher oestrogen. In this study, the researchers aimed to show how measures of facial symmetry and sexual dimorphism are related across Europeans, an African tribe and a non-human primate, i.e. whether symmetrical features were indicators of more masculine proportions in the male and more feminine proportions in the female.

The researchers collected photographs (taken in the laboratory) of 177 European males and 318 European females, who posed for their photograph with a neutral expression, i.e. a relaxed, unsmiling face. They were all UK university students between the ages of 17 and 29. The African images were of the Hadza people (67 males and 69 females) and were taken outdoors. The researchers selected those images that had the most neutral expression and where the individuals appeared to be young adults. For the non-human primate images, the researchers took outdoor photographs of a free-ranging population of rhesus macaques of Puerto Rico (105 males and 111 females).

From the photographs, the researchers estimated horizontal asymmetry by taking measurements of six pairs of points on the facial image (e.g. the inside edge of each eye) and their distance from the midline of the face. They also took measurements that indicated sexual dimorphism (e.g. prominence of cheekbones, size of the jaw etc.). They excluded the images which had excessive asymmetry which suggested that the head was tilted instead of being in a neutral position. They selected at random 50 images from each of the three groups (European, Hadza and macaque) and assessed the asymmetry and dimorphism in the images using a complex system of measurements.

The researchers then looked at whether the dimorphism of the images correctly predicted the person’s sex, and whether the accuracy of these predictions depended on how symmetrical the faces were. They then used the 15 most and least asymmetric faces among females and males to create six pairs of symmetric and asymmetric “composite” faces. In addition, they also created a set of control composite pairs made up from randomly selected faces. They asked a total of 87 volunteers to view the composite face pairs on a screen and rate which of the faces they thought to be most typical for that sex (depending on whether they were viewing a male or female pair). In these studies, only the face was viewed, without hair.

What were the results of the study?

Overall, the researchers found that faces correctly classified to their own sex, and therefore considered to be either more feminine or masculine, tended to be faces with higher symmetry. Asymmetric faces were more likely to be misclassified, e.g. a male’s face thought to be a female’s and vice versa.

In the composite tests, European female faces were thought to be more masculine the more asymmetric the face was and males were thought more masculine the less asymmetric the face was. The same trend was found for Hadza males but there were no significant trends seen for female faces. In macaque monkey faces, females were again thought more masculine the greater asymmetry there was in the face and males thought to be more masculine the less asymmetric the face was.

What interpretations did the researchers draw from these results?

The researchers conclude that symmetric faces are seen as being more sexually dimorphic in humans, of both a western society and those of a more tribal culture, and in a non-human primate. They say that there must be a “biological mechanism linking the two traits during development” and that the signalling properties of faces are universal across humans and non-humans.

What does the NHS Knowledge Service make of this study?

This research suggests that how symmetrical a face is may be linked to how feminine or masculine it is considered to be. However, the researchers do say that the measurements that they took may not have captured fully sexual dimorphism or symmetry.

This research has not investigated or suggested that increased facial symmetry, or “beauty” as the Telegraph describes it, is linked to better genes and that asymmetry is linked to less favourable genes. These are evolutionary theories that have been previously been suggested, mainly in the context of animal mating patterns and how what are considered to be favourable traits may have been passed onto future generations. The first line of the news article that “beautiful people are healthier and live longer” may or may not be the case, but as this research did not investigate this, it cannot add any evidence either way.

Sir Muir Gray adds...

instance of the headline not reflecting the story and the story not really reflecting the research.