Men looking for a quick fling prefer women with more "feminine" facial features, said a study Friday that delved into the evolutionary determinants of the mating game.

Feminine features like a smaller jawbone or fuller cheeks are closely linked to a woman's perceived attractiveness, which in turn is taken as an indicator of health, youth and fidelity and other traits, it said.

Feminine features are associated with a higher level of the female hormone oestrogen, which is also linked with reproductive success.

Studies on factors that influence human mating mostly focus on women, who have shown a similar preference for a hunkier man for a fling but a geekier one to settle down with -- possibly a more reliable bet for helping to raise children.

In a study with several hundred heterosexual male volunteers, a team of researchers made composite pictures of women's faces, and asked the men which ones they would choose for long- or short-term relationships.

There were two versions of each face -- one with slightly more feminine and the other more masculine features. The faces were taken from European or Japanese faces.

They found that men rated women with more feminine features more highly for a fling.

The preference was especially high among men who were already in a steady relationship.

"When a man has secured a mate, the potential cost of being discovered may increase his choosiness regarding short-term partners relative to unpartnered men, who can better increase their short-term mating success by relaxing their standards," wrote the study authors.

But in making long-term choices, men "may actually prefer less attractive/feminine women," they added.

Previous research has found that attractive women are likelier to be unfaithful, particularly if their partner is ugly.

"If his partner cheats on him, a man risks raising a child which is not his own," explained the authors.

The study, led by Anthony Little from the University of Stirling and Benedict Jones from the University of Glasgow, appears in the British Journal of Psychology.