Blue eyes -- A clue to paternity

Before you request a paternity test, spend a few minutes looking at your child's eye color. It may just give you the answer you're looking for. According to Bruno Laeng and colleagues, from the University of Tromso, Norway, the human eye color reflects a simple, predictable and reliable genetic pattern of inheritance. Their studies1, published this week in the Springer journal Behavioral Ecology and Sociobiology, show that blue-eyed men find blue-eyed women more attractive than brown-eyed women. According to the researchers, it is because there could be an unconscious male adaptation for the detection of paternity, based on eye color.

The laws of genetics state that eye color is inherited as follows:

1. If both parents have blue eyes, the children will have blue eyes.
2. If both parents have brown eyes, a quarter of the children will have blue eyes, and three quarters will have brown eyes.
3. The brown eye form of the eye color gene (or allele) is dominant, whereas the blue eye allele is recessive.

It then follows that if a child born to two blue-eyed parents does not have blue eyes, then the blue-eyed father is not the biological father. It is therefore reasonable to expect that a man would be more attracted towards a woman displaying a trait that increases his paternal confidence, and the likelihood that he could uncover his partner's sexual infidelity.

Eighty-eight male and female students were asked to rate facial attractiveness of models on a computer. The pictures were close-ups of young adult faces, unfamiliar to the participants. The eye color of each model was manipulated, so that for each model's face two versions were shown, one with the natural eye color (blue/brown) and another with the other color (brown/blue). The participants' own eye color was noted.

Both blue-eyed and brown-eyed women showed no difference in their preferences 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 blue-eyed female models as more attractive than brown-eyed models.

In a second study, a group of 443 young adults of both sexes and different eye colors were asked to report the eye color of their romantic partners. Blue-eyed men were the group with the largest proportion of partners of the same eye color.

According to Bruno Laeng and colleagues, "It is remarkable that blue-eyed men showed such a clear preference for women with the same eye color, given that the present experiment did not request participants to choose prospective sexual mates, but only to provide their aesthetic or attractiveness responses…based on face close-up photographs." Blue-eyed men may have unconsciously learned to value a physical trait that can facilitate recognition of own kin.

1. Laeng B et al (2006). Why do blue-eyed men prefer women with the same eye color? (Behavioral Ecology and Sociobiology, DOI 10.1007/s00265-006-0266-1)

Article is available to journalists as a pdf.

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