Tuesday, January 23, 2024

My wish list for 2024: Hormonal inputs into perception of human skin color by men and women


Subjects identify the face on the left as female and the face on the right as male. The only difference is the lightness of the skin. Richard Russell, Sinha Laboratory for Vision Research, MIT.


“The fair sex” is paler than men, who conversely are ruddier and browner than women. This sex difference seems to play a role in gender recognition and in relations between men and women, particularly in female response to darker male skin.


Women are universally the fair sex. They are paler than men, who conversely are ruddier and browner (Frost, 2010; Frost, 2023; van den Berghe and Frost, 1986). This sex difference is due to the differing ways the skin’s pigments—melanin, hemoglobin, carotene—interact with the sex hormones, either androgens in men or estrogens in women. A hormonal cause has been shown by studies of normal, castrated, and ovariectomized individuals, by studies of skin reflectance at puberty, and by studies of digit ratios (Edwards and Duntley, 1939; Edwards et al., 1941; Edwards and Duntley, 1949; Frost, 1988; van den Berghe and Frost, 1986; Manning et al., 2004).


Gender recognition


This sex difference is used subconsciously to recognize male and female faces (Frost, 2011; Russell, 2003; Russell, 2009; Russell, 2010; Russell et al., 2006; Semin et al., 2018).

Specifically, gender is identified from two aspects of facial color:


·         hue (men are ruddier and browner)

·         brightness (facial skin is lighter in women and contrasts more with the darker lip/eye area).


Hue provides the observer with a fast channel for gender recognition. If a face is too far away or the lighting too dim, the observer will switch to the slower but more accurate channel of brightness (Dupuis-Roy et al., 2009; Dupuis-Roy et al., 2019; Jones et al., 2015; Nestor and Tarr, 2008a; Nestor and Tarr 2008b; Tarr et al. 2001; Tarr, Rossion, and Doerschner, 2002). We thus perceive skin color through the lens of a mental algorithm that arose for gender recognition. This algorithm may explain why lighter skin seems more feminine and darker skin more masculine (Semin et al., 2018).


Male-female relations


The differing complexions of men and women play a role not only in gender recognition but also in relations between men and women. In particular, it seems to play a role in attraction by women to men.


In one study, women were asked to optimize the attractiveness of facial pictures by varying the skin's darkness and ruddiness. They made the male faces darker and ruddier than the female faces (Carrito et al., 2016). In another study, women were asked to rate different levels of male ruddiness. They associated high levels with aggression, medium levels with dominance, and low levels with attractiveness. Unlike the participants of the first study, they may have understood the term “attractive” in an aesthetic or even feminine sense (Stephen et al., 2012).

Female attraction to darker, ruddier male skin seems to be mediated by the level of estrogen in brain tissues. This estrogenic effect is shown by two studies of women at different phases of their menstrual cycle and by a study of preschool children:


·         Women were shown pairs of facial pictures that differed slightly in the lightness of the skin, and they were asked to choose the most pleasing one. When male faces were shown, the darker one was more strongly preferred by those women who were in the first two-thirds of their menstrual cycle than by those in the last third. During the first two-thirds of the cycle, the level of estrogen is high in relation to the level of progesterone (which acts as an anti-estrogen). During the last third, the ratio is reversed: the level of estrogen is low in relation to the level of progesterone. There was no cyclical effect among women judging female faces or taking oral contraceptives (Frost, 1994).


·         Women had their brain activity measured by MRI while viewing pictures of male faces. Their brains showed a stronger response to masculinized male faces than to feminized ones, and the strength of their response correlated with the level of estrogen across the menstrual cycle. In a personal communication, the lead author stated that the faces had been masculinized by making them darker and more robust in shape (Rupp et al., 2009).


·         Preschool boys and girls were presented with two dolls that differed slightly in skin color and asked to choose the “nicer” one. Their choices were recorded, as were measurements of their body mass index and their subcutaneous fat. Doll choice did not differ by sex. But it did differ by adiposity. Among children less than three years old, those who chose the darker doll had significantly more body fat than those who chose the lighter doll. In that age range, estrogen is produced mostly in the fatty tissues, which contain an enzyme (aromatase) that converts an androgen (androstenedione) into an estrogen (estrone) (Baird, 1976; Frost, 1989).



The doll on the right is slightly darker and ruddier than the one on the left. Among children below three years of age, those who chose the darker doll had significantly more body fat than those who chose the lighter doll. At such ages, estrogen is produced mainly in the body’s fatty tissues.


In other doll studies, boys and girls have similar preferences up to six years of age (Renninger and Williams, 1966; Williams and Roberson, 1967; Williams and Rousseau, 1971). At older ages, male and female preferences begin to diverge. When a group of American children, 3 to 8 years of age, were presented with a white-faced puppet and a brown-faced one, the latter puppet was more often chosen by girls than by boys, this finding being as true for Euro-American children as for African American children (Asher and Allen, 1969).


There are fewer controlled studies of male response to lighter female skin. It has been argued that the lighter skin of women mimics that of infants, whose pinkish color is especially noticeable in darker-skinned populations and, apparently, in other primate species. It seems to identify the primate infant as a vulnerable being in need of protection (Alley, 1980; Booth, 1962; Jay, 1962).


In our species, the adult female may have evolved a lighter complexion as a means to tap into the same behavioral response, the aim being not so much to increase male sexual arousal as to reduce male aggressiveness and stimulate feelings of care (Frost, 2010, p. 131-136; Frost, 2023; Guthrie, 1970).


Proposed study


First research aim: expand on Rupp et al. (2009) by using brain MRI to measure how women respond to male facial hue and luminosity in relation to the levels of estrogen and progesterone across the menstrual cycle. Male facial photos would be altered to produce different degrees of brownness, redness, and brightness.


Second research aim: repeat the doll study of Frost (1989) with direct measures of estrogen and androgen levels in preschool children. This may be difficult, given the low hormonal levels of early childhood (Baird, 1976; Klein et al., 1994).





Alley, T. R. (1980). Infantile colouration as an elicitor of caretaking behaviour in Old World primates. Primates 21(3): 416-429. https://doi.org/10.1007/BF02390470


Asher, S.R. and Allen, V.L. (1969). Racial preference and social comparison processes. Journal of Social Issues 25(1): 157-166. https://doi.org/10.1111/j.1540-4560.1969.tb02584.x    


Baird, D.T. (1976). Oestrogens in clinical practice. In: J.A. Loraine and E. Trevor Bell (eds.) Hormone assays and their clinical application (p. 408). Edinburgh: Churchill Livingstone.


Booth, C. (1962). Some observations on behavior of Cercopithecus monkeys. Annals of the New York Academy of Sciences 102(2): 477-487. https://doi.org/10.1111/j.1749-6632.1962.tb13654.x   


Bruce, V., and Langton, S. (1994). The use of pigmentation and shading information in recognising the sex and identities of faces. Perception 23(7): 803-822. http://dx.doi.org/10.1068/p230803   


Carrito, M.L., dos Santos, I.M.B., Lefevre, C.E., Whitehead, R.D., da Silva, C.F., and Perrett, D.I. (2016). The role of sexually dimorphic skin colour and shape in attractiveness of male faces. Evolution and Human Behavior 37(2): 125-133. https://doi.org/10.1016/j.evolhumbehav.2015.09.006    

Dupuis-Roy, N., Faghel-Soubeyrand, S., and Gosselin, F. (2019). Time course of the use of chromatic and achromatic facial information for sex categorization. Vision Research 157: 36-43. https://doi.org/10.1016/j.visres.2018.08.004   


Dupuis-Roy, N., Fortin, I., Fiset, D., and Gosselin, F. (2009). Uncovering gender discrimination cues in a realistic setting. Journal of Vision 9(2): 10, 1-8. https://doi.org/10.1167/9.2.10   


Edwards, E.A., and Duntley, S.Q. (1939). The pigments and color of living human skin. American Journal of Anatomy 65(1): 1-33. https://doi.org/10.1002/aja.1000650102   


Edwards, E.A., and Duntley, S.Q. (1949). Cutaneous vascular changes in women in reference to the menstrual cycle and ovariectomy. American Journal of Obstetrics & Gynecology 57(3): 501-509. https://doi.org/10.1016/0002-9378(49)90235-5   


Edwards, E.A., Hamilton, J.B., Duntley, S.Q., and Hubert, G. (1941). Cutaneous vascular and pigmentary changes in castrate and eunuchoid men. Endocrinology 28(1): 119-128. https://doi.org/10.1210/endo-28-1-119   


Frost, P. (1988). Human skin color: A possible relationship between its sexual dimorphism and its social perception. Perspectives in Biology and Medicine 32(1): 38-58. https://doi.org/10.1353/pbm.1988.0010


Frost, P. (1989). Human skin color: the sexual differentiation of its social perception. Mankind Quarterly 30: 3-16. http://doi.org/10.46469/mq.1989.30.1.1   


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(1): 507-14. https://doi.org/10.2466/pms.1994.79.1.507   


Frost, P. (2010). Femmes claires, hommes foncés. Les racines oubliées du colorisme. Quebec City: Les Presses de l'Université Laval, 202 p. https://www.pulaval.com/livres/femmes-claires-hommes-fonces-les-racines-oubliees-du-colorisme    


Frost, P. (2011). Hue and luminosity of human skin: a visual cue for gender recognition and other mental tasks. Human Ethology Bulletin 26(2): 25-34. https://www.researchgate.net/publication/256296588_Hue_and_luminosity_of_human_skin_a_visual_cue_for_gender_recognition_and_other_mental_tasks    


Frost, P. (2023). The original meaning of skin color. Aporia Magazine, February 7.


Guthrie, R.D. (1970). Evolution of human threat display organs. In T. Dobzhansky, M.K. Hecht, and W.C. Steere (Eds.) Evolutionary Biology 4: 257-302. New York: Appleton-Century Crofts.


Hill, H., V. Bruce, and Akamatsu, S. (1995). Perceiving the sex and race of faces: The role of shape and colour. Proceedings of the Royal Society B: Biological Sciences 261(1362): 367-373. https://doi.org/10.1098/rspb.1995.0161   


Hill, R., and Barton, R. (2005). Red enhances human performance in contests. Nature 435: 293. https://doi.org/10.1038/435293a   


Jay, P.C. (1962). Aspects of maternal behavior among langurs. Annals of the New York Academy of Sciences 102(2): 468-476. https://doi.org/10.1111/j.1749-6632.1962.tb13653.x


Jones, A.L., Russell, R., and Ward, R. (2015). Cosmetics alter biologically-based factors of beauty: evidence from facial contrast. Evolutionary Psychology 13(1): https://doi.org/10.1177%2F147470491501300113    


Klein, K.O., Baron, J., Colli, M.J., McDonnell, D.P., and Cutler, G.B. Jr. (1994). Estrogen levels in childhood determined by an ultrasensitive recombinant cell bioassay. Journal of Clinical Investigation 94(6): 2475-2480. https://doi.org/10.1172/JCI117616


Manning, J.T., Bundred, P.E., and Mather, F.M. (2004). Second to fourth digit ratio, sexual selection, and skin colour. Evolution and Human Behavior 25(1): 38-50. https://doi.org/10.1016/s1090-5138(03)00082-5   


Nestor, A., and Tarr, M.J. (2008a). The segmental structure of faces and its use in gender recognition. Journal of Vision 8(7): 7, 1-12, https://doi.org/10.1167/8.7.7   


Nestor, A., and Tarr, M.J. (2008b). Gender recognition of human faces using color. Psychological Science 19(12): 1242-1246. https://doi.org/10.1111/j.1467-9280.2008.02232.x   


Renninger, C.A. and Williams, J.E. (1966). Black-white color connotations and racial awareness in preschool children. Perceptual and Motor Skills 22(3): 771-785. https://doi.org/10.2466/pms.1966.22.3.771   


Rupp, H.A., James, T.W., Ketterson, E.D., Sengelaub, D.R., Janssen, E., and Heiman, J.R. (2009). Neural activation in women in response to masculinized male faces: mediation by hormones and psychosexual factors. Evolution and Human Behavior 30(1): 1-10. https://doi.org/10.1016/j.evolhumbehav.2008.08.006   


Russell, R. (2003). Sex, beauty, and the relative luminance of facial features. Perception 32(9): 1093-1107. http://dx.doi.org/10.1068/p5101   


Russell, R. (2009). A sex difference in facial pigmentation and its exaggeration by cosmetics. Perception 38(8): 1211-1219. https://doi.org/10.1068/p6331   


Russell, R. (2010). Why cosmetics work. In: R.B. Adams Jr., N. Ambady, K. Nakayama, and S. Shimojo (eds.) The Science of Social Vision, (pp. 186-203). New York: Oxford.

Russell, R., Sinha, P., Biederman, I., and Nederhouser, M. (2006). Is pigmentation important for face recognition? Evidence from contrast negation. Perception 35: 749-759. https://doi.org/10.1068%2Fp5490   


Semin, G.R., Palma, T., Acartürk, C., and Dziuba, A. (2018). Gender is not simply a matter of black and white, or is it? Philosophical Transactions of the Royal Society B Biological Sciences 373(1752):20170126. https://doi.org/10.1098/rstb.2017.0126    


Siiteri, P.K. and MacDonald, P.C. (1973). Role of extraglandular estrogen in human endocrinology. In: S.R. Geiger (ed.), Handbook of Physiology, vol. II, Part 1, (pp. 615-629). Washington D.C.: American Physiology Society, Section 7.


Stephen, I.D., Oldham, F.H., Perrett, D.I., and Barton, R.A. (2012). Redness enhances perceived aggression, dominance and attractiveness in men's faces. Evolutionary Psychology 10(3). https://doi.org/10.1177%2F147470491201000312   


Tarr, M.J., Kersten, D., Cheng, Y., and Rossion, B. (2001). It's Pat! Sexing faces using only red and green. Journal of Vision 1(3): 337, 337a. https://doi.org/10.1167/1.3.337   


Tarr, M. J., Rossion, B., and Doerschner, K. (2002). Men are from Mars, women are from Venus: Behavioral and neural correlates of face sexing using color. Journal of Vision 2(7): 598, 598a, https://doi.org/10.1167/2.7.598   


Trivers, R., Manning, J., and Jacobson, A. (2006). A longitudinal study of digit ratio (2D:4D) and other finger ratios in Jamaican children. Hormones and Behavior 49(2): 150-156. https://doi.org/10.1016/j.yhbeh.2005.05.023     


van den Berghe, P. L. and P. Frost. (1986). Skin color preference, sexual dimorphism, and sexual selection: A case of gene-culture co-evolution? Ethnic and Racial Studies 9(1): 87-113. https://doi.org/10.1080/01419870.1986.9993516


Williams, J.E. and Roberson, J.K. (1967). A method for assessing racial attitudes in preschool children. Educational and Psychological Measurement 27(3): 671-689. https://doi.org/10.1177/001316446702700310   


Williams, J.E. and Rousseau, C.A. (1971). Evaluation and identification responses of Negro preschoolers to the colors black and white. Perceptual and Motor Skills 33(2): 587-599. https://doi.org/10.2466/pms.1971.33.2.587   


Chris Crawford said...

The question on my mind is WHY men are darker and ruddier than women? What evolutionary forces could have produced this result? It seems unlikely to have arisen to facilitate gender recognition. The only explanatory hypothesis I can imagine is that it is a consequence of hominem males spending more time in the sun that females, thus requiring a larger dose of melanin in the skin. But I would not bet any money on that hypothesis.

Peter Frost said...

Male skin colour is the default. It's what you would expect if the only selection pressures were solar UV and perhaps release of excess body heat. Female skin has become lighter as a means to exploit mental algorithms that reduce male aggressiveness and induce a desire to defend and provide care.

Daniel said...

I saw this response by Kevin Byrd can you respond to it This is some embarrassing flailing. I document several misrepresentations and inaccuracies in your video. The claims about the cause of the Flynn effect decline and the relationship of g-loaded IQ subtests and culture were just two direct refutations. You seem very confused about the fact 84% of genes are expressed somewhere in the brain at some point during development. This has no implication for racial differences unless you can specifically identify expression differences between races and their relationship to IQ. This research has not and likely cannot be done and the genetic data I presented shows there is no evidence of substantial genetic differences between races for genes associated with intelligence when you correct for biases in GWAS engage with your references the whole time, and bring up studies that address the crucial weaknesses in your cited work. It's a literature review based on some of the latest genetic studies and on economic papers that correct for the shoddy statistical analyses used in much of the IQ literature. It isn't the "sociologist's fallacy" to show that accounting for these socioeconomic differences reduces the gaps since there is strong evidence and historical documentation that these socioeconomic differences between races are not genetic themselves and again no evidence from that genetics contributes to these racial gaps. Bringing up the Coleman report is irrelevant when I present papers from this decade (not half a century ago) showing that data from 4 million students pointing toward economic inequality and segregation as driving the majority of achievement test score gap in schools. You should update your references to the proper century. Now addressing the rest of your tantrum in order: 1. Yes, correlational research is weak and needs either experimental validation or more robust methods to infer causality. 2. They are fundamentally interactions, they are not separable as genetic or environmental and they show that phenotypes can change in different environments. 3. Laughing does not refute my own published researcher showing that genes associated with intelligence do not show the patterns that would be present if natural selection were acting to make Europeans more intelligent than Africans. 4. Your evidence for dysgenics relies on faulty genetic methods prone to false-positives and from researchers with no credibility or expertise. 5. The sibling study on the Flynn is precisely the kind of well-designed study that can distinguish genetic from environmental causes and it unambiguously supports environment and precludes genetic causes. 6. Fst between dog breeds are much larger than between human populations. The paper I cited references 3-5% for human races and 27% for dogs using comparable genetic markers. 7. The distinction between within- and between group heritability is a fundamental aspect of that statistical method. Also the data I presented did show school districts where there are no racial test score gaps, a closing racial test score gap for national standardized tests, and IQ tests which show no racial gap.