BLUE-eyed men prefer blue-eyed women, apparently because eye colour can help reveal whether their partner has been faithful, researchers say.Behavioral Ecology and Sociobiology (online first)
"Before you request a paternity test, spend a few minutes looking at your child's eye colour," Bruno Laeng and colleagues at the University of Tromso in Norway said in the study.
Under the laws of genetics, two parents with blue eyes will always have blue-eyed children, it said. So a blue-eyed man can know his blue-eyed wife or partner has cheated on him if their child has brown eyes.
"Blue-eyed men may have unconsciously learned to value a physical trait that can facilitate recognition of own kin," the scientists said in the journal Behavioural Ecology and Sociobiology.
The scientists asked 88 students to rate the attractiveness of models based on pictures manipulated so that half of them had blue eyes and the other half had brown eyes.
The blue-eyed men in the group showed a preference for blue-eyed women.
But brown-eyed men, who cannot find any clues about paternity from a child's eye colour, had no preferences by eye colour.
Women showed no preference for brown or blue-eyed men, irrespective of their own eye colour.
A quarter of children born to two brown-eyed parents who have both brown and blue-eye genes among their ancestors will have blue eyes. The rest will be brown.
In a second study, 443 young adults of both sexes were asked about the eye colour of their partners – blue-eyed men were also the group with the highest proportion of partners with the same eye colour.
Why do blue-eyed men prefer women with the same eye color?
Bruno Laeng et al.
Abstract The human eye color blue reflects a simple, predictable, and reliable genetic mechanism of inheritance. Blue-eyed individuals represent a unique condition, as in their case there is always direct concordance between the genotype and phenotype. On the other hand, heterozygous brown-eyed individuals carry an allele that is not concordant with the observed eye color. Hence, eye color can provide a highly visible and salient cue to the child’s heredity. If men choose women with characteristics that promote the assurance of paternity, then blue-eyed men should prefer and feel more attracted towards women with blue eyes. To test these predictions, close-up photos of young women and adult men with either blue or brown eyes were rated for their attractiveness by young women and men observers with either blue or brown eyes (N=88). The eye color in the photographs of each model was manipulated so that a same face would be shown with either the natural eye color (e.g., blue) or with the other color (e.g., brown). Both blue-eyed and brown-eyed female participants showed no difference in their attractiveness ratings for male models of either eye color. Similarly, brown-eyed men showed no preference for either blue-eyed or brown-eyed female models. However, blue-eyed men rated as more attractive the blue-eyed women than the brown-eyed ones. We interpret the latter preference in terms of specific mate selective choice of blue-eyed men, reflecting strategies for reducing paternity uncertainty. In a second study, a group of young adults (N=443) of both sexes and different eye colors (blue, brown, and green) were asked to report the eye and hair color of their romantic partners. Their responses indicated the presence of assortative mating by eye color as well as, to a less degree, for hair color. Most importantly, blue-eyed male respondents were the group with the largest proportion of partners of same eye color. These findings 1) indicate that blue-eyed men do prefer women with the same eye color and 2) specifically suggest the presence of a male adaptation for the detection of extra-pair paternity based on eye color, as a phenotypically based assurance of paternity (i.e., when the father’s and offspring’s phenotypes match) as well as a defense against cuckoldry (i.e., when the phenotypes do not match).