Asymmetry could account for a fifth of the variation in romantic jealousy from person to person, says a Canadian researcher.

Just about everyone is lopsided to some extent. Hormone imbalances in the womb, for instance, can lead to one foot being bigger than the other. But in recent years, a series of animal and human studies have suggested that the implications of asymmetry go far beyond struggling to find shoes that fit both feet.

It seems that people who are more symmetrical are not only healthier, more fertile and perhaps even smarter - they are also more attractive.

This led William Brown at Dalhousie University in Halifax, Nova Scotia, to wonder about jealousy. "If jealousy is a strategy to retain your mate, then the individual more likely to be philandered on is more likely to be jealous," he speculated. And if people who are less symmetrical are less desirable, they are more likely to be cheated on.

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