Why beauty is an advert for good genes?

Beautiful people are healthier and live longer, according to a study of sex appeal.
The discovery has come from research conducted across cultures and species that focused on one trait that earlier work found was attractive: symmetry.
No one disputes that symmetrical faces, such as that of Kate Moss, are more attractive.
But why? One idea is that the trait is an advert of genetic quality or fertility.
An alternative view is that preferences for a symmetrical face arose from cultural factors and say nothing about health, fecundity and other biological factors.
Now support for the idea that a symmetrical face is indeed a strong advert of mate ‘quality’ is published today in the journal PLoS One by Dr Anthony Little of the University of Stirling and colleagues.
Using mug shots of Europeans, the Hadza of Tanzania, one of the last hunter gatherer cultures, and macaque monkeys, measurements were made and people were asked to judge the masculinity of the most and least symmetric pictures.
Whether a member of a troop or a tribe, symmetric males had more masculine facial proportions and symmetric females had more feminine facial proportions.
"In humans, if you look at female models, for example, they tend to be pretty symmetric and at the extremes of femininity," Dr Little says.
He adds "One good face trait deserves another - symmetric men and women appear to have other good face traits".
The findings back the claim that the masculinity/femininity of faces is linked with symmetry and hence advertise quality, that is good genes.
Biological quality can mean many things but as symmetry and femininity/masculinity arise during development then one explanation for the findings is that "both traits could advertise quality in terms of resistance to disease, or environmental stresses and that might mean people with these traits are healthier and live longer," says Dr Little.
We seek a partner with good looks because this is a biological advert that says good genes are to be found in this particular body to help our own genes thrive in the next generation.
He adds that a second paper in the journal Behavioural Ecology shows that people who prefer more symmetric faces prefer more extreme faces, that is a rugged male face or a beautiful feminine female face.
Dr Little concludes that "overall our work suggests that symmetry and masculinity in faces signal the same thing and that these signals are present across human populations and also in our non-human primate relatives."

The researchers are still collecting data on facial beauty at www.alittlelab.com

Roger Highfield, Science Editor