Romantics may tell us that opposites attract, but, according to scientists, if you find yourself irresistibly drawn to someone who looks nothing like you, it may mean that you've been working too hard. A study published  online this week in the Proceedings of the Royal Society B suggests that men under stress are more likely to find physically dissimilar women attractive.
Previous research has shown that couples tend to have similar facial characteristics. Some evolutionary biologists suggest this is because we subconsciously see people who look like us as more trustworthy. However, research in animals has shown that individuals under stress are willing to mate with a wider variety of partners. Experimental psychologist Johanna Lass-Hennemann and colleagues at the University of Trier, Germany, wondered whether this might also be true for people.
They recruited 50 male students and instructed half of them to hold their right hand in ice water for 3 minutes, a harmless but effective form of stress. They then showed each subject a series of photographs of nude women. Unbeknownst to the young men, some of the images had been subtly modified—the women's faces had been morphed with a picture of the subject's face to produce an image that, although still apparently feminine, had a subtle resemblance to the subject himself. While looking at the pictures, each man experienced a brief burst of intense white noise. Electrodes attached to his face measured how much he flinched on hearing the sound. This is a well-established method of measuring instinctive attraction to an image, given that those in a more upbeat frame of mind flinch less.
As predicted, unstressed subjects were more attracted to the doctored images that resembled their own faces. Stressed subjects, however, actively favored the original pictures that were less familiar. "This was not exactly expected," says Lass-Hennemann.
The team suspect that the explanation may lie in evolutionary biology. Humans, like other animals, strive for the survival of their genes into future generations. When conditions seem favorable, the researchers suggest, men have the option of picking physically similar mates, whom they subconsciously deem dependable partners who will nurture their offspring. But in stressful times, during which human survival is less guaranteed, men would be more willing to risk a physically dissimilar partner in order to father as many children as possible.
The team want to investigate the phenomenon further. At the top of their list is finding out whether female sexual preferences are affected in the same way. "In theory, women should be more choosy than men in mating decisions because they don't have the opportunity to reproduce as much," says Lass-Hennemann.
Fellow experimental psychologist Ben Jones of Aberdeen University in the United Kingdom considers the findings meaningful but questions whether the difference in instinctive attraction is sexual in nature. "The authors make very strong claims about the effect of self-resemblance on mate preference," says Jones. He points to previous research suggesting that people's reactions to familiar and unfamiliar faces differ even more widely when those faces belong to individuals of the same sex, perhaps because they subconsciously see resemblance to family members in similar faces.