The Science of Sex

Tuesday, April 7th, 2009

A naked woman from behind

Jon Purdy

Is there a magic formula for sexual attraction?

Evolutionary psychology suggests physical attractiveness provides biological information about disease, fertility and genetic quality.

Evolutionary psychologists are researching the role of face and body symmetry, waist-to-hip and shoulder-to-waist ratio and masculinity and femininity in sexual attraction.


• If you divide the body in half, both sides should match up

• People who have weak immune systems tend to be less symmetrical

• Most people’s faces are slightly asymmetrical, but both sexes find symmetrical faces more attractive

• Symmetrical people have good genes that can be passed onto their children

• Body symmetry may also predict women’s estrogen levels


Hip-to-waist ratio, a well-documented fertility trait, is calculated by dividing waist measurement by hip measurement. It’s not about weight, but weight distribution.

• Men place more importance on youth and beauty, which is related to fertility

• Studies show men prefer women with feminine waists and the optimal waist-to-hip ratio

• Males prefer a 0.7 waist-to-hip ratio " the waist is 70 per cent the size of the hips " which is a curvy appearance

• Females prefer a 0.9 waist-to-hip ratio and no higher than 1.0

• Females prefer males with broad shoulders and average waist-to-hip ratios, which forms a “V” shape


Masculine faces tend to be longer, have broader chins and stronger brow ridges. Feminine faces tend to have smaller jaws and noses, and larger eyes and lips.

• Generally, males prefer femininity in women’s faces and bodies

• Some females prefer masculinity and others femininity in men’s facial features

• Muscularity and facial masculinity require large amounts of testosterone, which is hard on the immune system

• Masculine men are higher risks as stable long-term partners

• Women seeking stability tend to be more attracted to more “caring” men with somewhat feminine faces


Pheromones or body odour are more important than most people realize.

• Some studies show women consider a man’s odour the most important attribute in determining relationship status

• Research indicates both sexes are attracted to the scent of people who don’t share a similar genetic makeup

• Symmetry and pheromones are related traits; certain physical cues indicate genetic quality symmetry

Example: In one study, men wore T-shirts for several nights without wearing deodourant or washing. Women rated the “pleasantness” of the T-shirts’ smell without seeing the men. Women considered the more symmetrical men’s T-shirt scents more pleasing " but only when they were at or near ovulation.


• Ovulation creates subtle changes in women’s faces, scent and behaviour

• Studies suggest women are unconsciously motivated to have sex when they are fertile and thus might dress sexier

• It’s also suggested ovulating women fertile in their cycle find masculine, more dominant men particularly sexy

Test your preferences and help with sex research by visiting and

Sources: Dave Frederick, psychology graduate student at the University of California; Devendra Singh, psychology professor at the University of Texas; Lorne Campbell, psychology professor at Western; David Perrett, psychology professor at the University of St. Andrews; Steven Gangestad, psychology professor at the University of New Mexico

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