Jealous lovers will wish they could adjust the height of their heels, for the power of the green-eyed monster depends on how tall you are.

So say researchers from the Universities of Groningen and Valencia who asked 549 men and women in the Netherlands and Spain to rate how jealous they felt and to identify the qualities in a romantic competitor that were most likely bug them.

Men, who generally felt most nervous about attractive, rich and strong rivals, were increasingly relaxed, the taller they were themselves. Women, on the other hand, were most jealous of others' beauty and charm, but least so if their own height was average.

This makes evolutionary sense, say the researchers, because previous findings suggest that whilst taller men do best with the ladies, it is women of medium height who enjoy the best health, fertility and popularity with men.

But unlike tall men, medium-height women can be more vulnerable to jealousy under some circumstances. Faced with socially or physically powerful rivals they actually felt more jealous than shorter or taller women. According to the study, this may be because tall and strong, or socially well-connected women could well pose a threat to average-height feminine favourites since they might win conflicts, including physical fights. "Taller women are more dominant and have greater fighting abilities than shorter women," write the researchers in Evolution and Human Behavior (vol 29, p 133).