Averaged face of blue-eyed male subjects (left). Averaged face of brown-eyed male subjects (right). Czech population. (Kleisner et al., 2010)
Karel Kleisner’s team is continuing its work on eye color, face shape, and perceived personality traits:
We tested whether eye color influences perception of trustworthiness. Facial photographs of 40 female and 40 male students were rated for perceived trustworthiness. Eye color had a significant effect, the brown-eyed faces being perceived as more trustworthy than the blue-eyed ones. Geometric morphometrics, however, revealed significant correlations between eye color and face shape. Thus, face shape likewise had a significant effect on perceived trustworthiness but only for male faces, the effect for female faces not being significant. To determine whether perception of trustworthiness was being influenced primarily by eye color or by face shape, we recolored the eyes on the same male facial photos and repeated the test procedure. Eye color now had no effect on perceived trustworthiness. We concluded that although the brown-eyed faces were perceived as more trustworthy than the blue-eyed ones, it was not brown eye color per se that caused the stronger perception of trustworthiness but rather the facial features associated with brown eyes. (Kleisner et al., 2013)
Eye color is thus associated in males with a specific face shape, even when the men are of the same ethnic background, i.e., Czechs in this study. Face shape is more robust if eye color is brown and less so if eye color is blue. Furthermore, a robust male face seems to evoke an image of dominance and trustworthiness, whereas a less robust one is perceived as being less dominant and less trustworthy.When the first study came out, in 2010, I thought this association between eye color and face shape was due to ethnic admixture, i.e., some of the brown-eyed participants had Jewish or Roma ancestry. If this were so, however, face shape would vary to a greater degree among the brown-eyed participants than among the blue-eyed ones, yet the current study found no such difference. The “ethnic admixture” explanation also fails to explain why blue eyes are associated with a less robust face in men but not in women.
Are European facial features actually female facial features?There thus seems to be a linkage between eye color and face shape. This finding is consistent with findings for other European physical traits, especially bright or colorful facial features. These European traits—white skin, multi-colored hair, multi-colored eyes, and a less robust face shape—are actually female traits. They seem to be due to a selection pressure that first acted on early European women and then spilled over on to early European men. This phenotypic change affected both sexes because the traits in question are at most mildly sex-linked.
The direction of sex linkage is consistent with the above model of selection. Hair color became polymorphic in Europeans through the emergence of brighter hues, but this evolutionary change is most pronounced in European women. According to a twin study, hair is lighter in women than in men, with red hair being especially more common. Women also show more variation in hair color (Shekar et al., 2008). Again, this evolutionary trend seems to have been driven by European women with European men tagging along.
There is also unpublished evidence that “European” hair and eye colors (i.e., non-black hair and non-brown eyes) are associated with a higher degree of estrogenization before birth, as indicated by digit ratio. This prenatal estrogenization might also favor a more feminine face shape. Face shape would thus correlate with eye color because of a shared determining factor: the degree to which the fetus is estrogenized or androgenized in the womb. Such a correlation would have been stronger in the male participants than in the female participants because estrogenization is overdetermined in females, i.e., almost all girls are exposed to enough estrogen in the womb to feminize their face shape, whereas this level of estrogenization would be reached only in blue-eyed boys.
In one respect, however, the blue-eyed face looks less feminized, the chin being relatively narrower and longer. It might be that this is what happens when the trajectory of facial development is initially programmed for a feminine appearance before birth but is not supported by circulating estrogen later in life.
ReferencesFrost, P. (2008). Sexual selection and human geographic variation, Special Issue: Proceedings of the 2nd Annual Meeting of the NorthEastern Evolutionary Psychology Society. Journal of Social, Evolutionary, and Cultural Psychology, 2(4),169-191. http://126.96.36.199/jsec/articles/volume2/issue4/NEEPSfrost.pdf
Frost, P. (2006). European hair and eye color - A case of frequency-dependent sexual selection? Evolution and Human Behavior, 27, 85-103 http://www.sciencedirect.com/science/journal/10905138
Kleisner, K., L. Priplatova, P. Frost, & J. Flegr. (2013). Trustworthy-looking face meets brown eyes, PLoS One, 8(1): e53285. doi:10.1371/journal.pone.0053285http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053285
Kleisner, K., T. Kočnar, A. Rubešova, and J. Flegr. (2010). Eye color predicts but does not directly influence perceived dominance in men, Personality and Individual Differences, 49, 59–64.
Shekar, S.N., D.L. Duffy, T. Frudakis, G.W. Montgomery, M.R. James, R.A. Sturm, & N.G. Martin. (2008). Spectrophotometric methods for quantifying pigmentation in human hair—Influence of MC1R genotype and environment. Photochemistry and Photobiology, 84, 719–726.