The subjects were presented with photos of male or female faces, one at a time, and asked to give the faces an optimal healthy appearance. This was done by manipulating the facial complexion on a continuum ranging from red (color of oxygenated blood) to dark blue (color of deoxygenated blood). To varying degrees, the subjects preferred to redden the faces, but this effect was stronger with female faces than with male ones.
At first glance, this sex difference seems counterintuitive. Women are the ‘fair sex’ while men are ruddier and browner in complexion (Edwards & Duntley, 1939). Why, then, would a ruddy complexion be considered more appropriate for a female face than for a male one?
The problem may be that the researchers measured responses only to colors ranging from red to dark blue. No other colors were tested. So the visual cue could be luminosity rather than hue. In other words, the subjects may have more strongly associated red with femininity because red is lighter than dark blue. This point is hinted at in the press release:
Professor Dave Perrett, head of the Perception Lab commented, "Our evaluators all thought that bright red blood with lots of oxygen looked healthier than darker, slightly bluer blood with lower oxygen levels. It is remarkable that people can see this subtle difference.
Curiously, the same press release describes the ‘deoxygenated’ face as ‘pale’. To my eyes, the ‘oxygenated’ face is clearly the one with the lighter hue.
There is in fact a large body of cross-cultural and psychological research showing that people associate lighter skin tones with women and darker ones with men (Feinman & Gill, 1978; Frost, 1994; Osgood, 1960; Russell, 2003; Russell & Sinha, 2007; Russell et al., 2006; Tarr et al., 2001, van den Berghe & Frost, 1986). Could this mental association explain why the feminine ideal is more pink than blue?
I suspect the researchers were surprised by the sex difference in their findings. In the ‘Discussion’ section, they suggest that ruddiness, and hence greater blood circulation, is more adaptive for women than for men, given that female blood has a lower oxygen content. If this were so, however, wouldn’t natural selection cause women to become ruddier than men? This is the opposite of what we see.
It would be more parsimonious to attribute this sex difference in response to a sex-identification algorithm, rather than to a health-assessment algorithm.
References
Edwards, E.A., & Duntley, S.Q. (1939). The pigments and color of living human skin. American Journal of Anatomy, 65, 1-33.
Feinman, S. & G.W. Gill. (1978). Sex differences in physical attractiveness preferences, Journal of Social Psychology, 105, 43-52.
Frost, P. (1994). Preference for darker faces in photographs at different phases of the menstrual cycle: Preliminary assessment of evidence for a hormonal relationship, Perceptual and Motor Skills, 79, 507-514.
Osgood, C.E. (1960). The cross-cultural generality of visual-verbal synthesthetic tendencies, Behavioral Science, 5, 146-169.
Russell, R. 2003. Sex, beauty, and the relative luminance of facial features, Perception, 32, 1093-1107.
Russell, R. & P. Sinha. 2007. Real-world face recognition: The importance of surface reflectance properties, Perception, 36, 1368-1374.
Russell, R., P. Sinha, I. Biederman & M. Nederhouser. 2006. Is pigmentation important for face recognition? Evidence from contrast negation. Perception, 35, 749-759.
Stephen, I.D., Coetzee, V., Law Smith, & M., Perrett, D.I. (2009) Skin Blood Perfusion and Oxygenation Colour Affect Perceived Human Health. PLoS ONE, 4(4), 1-7
e5083. doi:10.1371/journal.pone.0005083
Tarr, M.J., D. Kersten, Y. Cheng & B. Rossion. (2001). It's Pat! Sexing faces using only red and green, Journal of Vision, 1(3), http://journalofvision.org/1/3/337.
van den Berghe, P. L. & P. Frost. (1986). Skin color preference, sexual dimorphism, and sexual selection: A case of gene-culture co-evolution?, Ethnic and Racial Studies, 9, 87-113.