The original meaning of skin color

Averaged female face (left) and averaged male face (right). (Dupuis-Roy et al. 2009)

At puberty the skin differentiates between the sexes, including its color. Men are browner and ruddier, having more melanin and blood in their skin. By comparison, women are "the fair sex" (Edwards and Duntley 1939; Edwards and Duntley 1949; Edwards et al. 1941; Frost 1988; Frost 2010; Frost 2011; Kalla 1973; Manning et al. 2004; Mazess, 1967; van den Berghe and Frost 1986). Women also display a higher luminous contrast between their facial skin and their lips and eyes (Dupuis-Roy et al. 2009).

In most Western societies this sex difference is scarcely noticeable, being overwhelmed by the much larger differences of race and ethnicity. It has been further obscured since the 1920s by the popularity of tanning among many Western women (Segrave 2005). Nonetheless, for most of human history and prehistory it has been the main reason why skin color varies in our immediate visual environment.

The human mind tends to hardwire any mental task that comes up repeatedly. It thereby shortens response time and eliminates learning time. One such task is to identify whether a person is a man or a woman by examining certain features, such as face shape and properties of the skin, including pigmentation. So when we see the minor pigmentary differences that distinguish men and women, does an innate mechanism process that visual information? This question takes us to research on the best-known example of hardwiring.

Face recognition, gender identification, and facial color

We have an innate ability to recognize human faces. This is shown by a form of brain damage called prosopagnosia, where one may seem normal and yet be no better at recognizing a face than any other object (Farah 1996; Pascalis and Kelly 2008; Zhu et al. 2009). At the other extreme are "super-recognizers" who are as good at face recognition as prosopagnosics are bad (Russell, Duchaine, and Nakayama 2009). 

This mental mechanism is sexually differentiated to some degree. It encompasses several neural populations, some of which specialize in male faces, others in female faces, and others in both kinds indifferently (Baudouin and Brochard. 2011; Bestelmeyer et al. 2008; Jacquet and Rhodes 2008; Little et al. 2005).

To tell male and female faces apart, this mechanism seems to use facial color (Bruce and Langton 1994; Hill, Bruce, and Akamatsu 1995; Russell and Sinha 2007; Russell et al. 2006; Tarr et al. 2001; Tarr, Rossion, and Doerschner 2002). The criteria are hue (brownness and ruddiness) and luminosity (lightness of the skin versus darkness of the lip/eye area). Hue is a fast "channel" for gender identification (Dupuis-Roy et al. 2009; Nestor and Tarr 2008a; Nestor and Tarr 2008b; Tarr et al., 2001; Tarr, Rossion, and Doerschner 2002). If the observer is too far away or the lighting too dim, the brain switches to the slower but more accurate channel of luminosity (Dupuis-Roy et al. 2009).

When shown a human face, subjects can tell its gender even if the image is blurred and differs only in color (Tarr et al. 2001). Indeed, facial color seems especially crucial under conditions of poor visibility when face shape is uncertain (Yip and Sinha 2002). 

The existence of a hardwired mental mechanism may explain not only why a certain schema of facial color is unthinkingly identified as female but also why women seek to accentuate this schema in a wide range of cultures. Thus, in different parts of the world, female cosmetics have shared the same aim of increasing the contrast between facial color and lip/eye color (Russell 2003; Russell 2009; Russell 2010). In a similarly wide range of cultures, women have tried to lighten their color by avoiding the sun and wearing protective clothing (Frost 2010, pp. 120-123). Going back to earliest times, we see that lighter skin was a female norm wherever the visual arts had developed—in ancient Greece, in ancient Egypt, in ancient China and Japan, and in Mesoamerica. All of these artistic traditions systematically gave a lighter coloring to female figures than to male figures (Capart 1905, pp. 26-27; Eaverly 1999; Soustelle 1970, p. 130; Tegner 1992; Wagatsuma 1967).

A cue for sexual interest

In addition to identifying gender, facial color can arouse sexual interest, being linked to gendered notions of attractiveness. 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 shown pairs of facial pictures where one face was slightly darker than the other, and they had to choose the most pleasing one. When male faces were shown, the darker face was more strongly preferred by women in the first two-thirds of their menstrual cycle (high estrogen/progesterone ratio) than by women in the last third (low estrogen/progesterone ratio). There was no cyclical effect if the women were judging female faces or taking oral contraceptives (Frost 1994).

The above findings are consistent with the results of a brain-imaging study: the female subjects had a stronger neural response to pictures of "masculinized" male faces, and this response correlated with their estrogen level across the menstrual cycle (Rupp et al. 2009). In a personal communication, the lead author stated that the faces had been masculinized by making them darker and more robust in shape.

A cue for modifying emotions and behavior

Facial color can elicit other responses. In word-association tests, the lighter complexion of women brings to mind such words as innocence, purity, peace, chastity, modesty, femininity, and delicacy (Gergen 1967; Wagatsuma 1967). This sort of response likewise emerged during interviews with Japanese men: "Whiteness is a symbol of women, distinguishing them from men." "Whiteness suggests purity and moral virtue." "One's mother-image is white" (Wagatsuma 1967, pp. 417-418).

Infants too are lighter-skinned (Grande et al. 1994; Kalla 1973; Post et al. 1976). They also share other visual, auditory, and tactile cues with the adult female body: a smaller nose and chin; a higher pitch of voice; and smoother, less hairy, and more pliable skin. This is what Konrad Lorenz dubbed the Kindchenschema, which seems to have the property of reducing aggressiveness in adults and eliciting care and nurturance (Frost 2010, pp. 134-135; Grande et al. 1994; Lorenz 1971, pp. 154-164). 

Infants are light-skinned in other primates. This is particularly so with langurs, baboons, and macaques, whose skin is pink in newborns and almost black in adults. The distinct infant coloration not only helps parents find wayward offspring but also elicits caregiving and defensive reactions. As it disappears with age, infants no longer attract the same interest and are less often sought out and held by adult females (Alley 1980; Alley 2014; Blaffer-Hrdy 2000, pp. 446-448; Booth 1962; Jay 1962). 

In humans, this infant coloration is striking in dark-skinned peoples. In Kenya, newborn children are often called mzungu ("European" in Swahili), and a new mother may tell her neighbors to come and see her mzungu (Walentowitz 2008). Among the Tuareg, children are said to be born "white" because of the freshness and moisture of the womb (Walentowitz 2008). The cause is often thought to be a previous spiritual life:

There is a rather widespread concept in Black Africa, according to which human beings, before "coming" into this world, dwell in heaven, where they are white. For, heaven itself is white and all the beings dwelling there are also white. Therefore the whiter a child is at birth, the more splendid it is. In other words, at that particular moment in a person's life, special importance is attached to the whiteness of his colour, which is endowed with exceptional qualities. (Zahan 1974, p. 385)

Another Africanist makes the same point: "black is thus the color of maturity [...] White on the other hand is a sign of the before-life and the after-life: the African newborn is light-skinned and the color of mourning is white kaolin" (Maertens 1978, p. 41).


Evolution of women's lighter skin

The above suggests that lighter coloration, as a social signal, went through four stages of evolution:

1. Initially, newborn primates were light-skinned because they had no need for pigment in the womb.

2. Adults recognized light skin as a mark of infancy. Selection then favored hardwiring of certain behavioral and emotional responses, particularly by females and to a lesser extent by all members of the local group. This mechanism could nonetheless be overridden by strange males that invade the group and kill the young (Alley 1980).

3. The same selection pressure caused infants to remain lighter-colored until they no longer had to be cared for. This was particularly so in those species where care of offspring was greater and lasted longer.

4. In humans, slower maturation, higher paternal investment, and longer-lasting pair bonds increased the risk of male neglect and aggression, thus creating a similar selection pressure and causing women to mimic key features of the Kindchenschema.

This evolutionary path was described by the ethologist Russell Guthrie:

I believe the sexual differences in skin color resulted from female whiteness being selected for because it is opposite the threat coloration, although the selection pressures may have been rather mild. Light skin seems to be more paedomorphic, since individuals of all races tend to darken with age. Even in the gorilla, the most heavily pigmented of the hominoids, the young are born with very little pigment. [...] Thus, a lighter colored individual may present a less threatening, more juvenile image. (Guthrie 1970)

From this perspective, women acquired a lighter color to modify rather than arouse sexual interest. This hypothesis is supported by a two-part study where men were first shown pictures of women and asked to rate their attractiveness. Lighter-skinned women were not rated more attractive than darker-skinned women. In the second part, eye movements were tracked, and it was found that lighter-skinned women were viewed for a longer time than darker-skinned women. The longer duration may indicate a slower rise and fall in sexual interest (Garza et al. 2016). 

By altering the trajectory of sexual interest, women's lighter skin may modify male behavior by dampening strong emotions, like aggression, and inducing feelings of care. This is perhaps a clue to why many women embraced the tanned look during the 20th century, in defiance of older norms of femininity. The new look enabled them to exploit an erotic sensibility that had earlier been stigmatized. In Victorian-era novels the "dark lady" is an "impetuous," "ardent," and "passionate" object of short-lived romances (Carpenter 1936, p. 254). Similarly, in French novels of the same period "[t]he love incarnated by brown women appears as the conceptual equivalent of a devouring femininity, thus making them similar to the mythical figure of Lilith" (Atzenhoffer, 2011, p. 6).This motif goes back at least to the Middle Ages in various European cultures and highlights an alternate form of eroticism:

[...] dark girls [...] are inevitably imagined as sexually more available than their fairer sisters, with whom they are implicitly or explicitly contrasted. In addition, the change of a girl's complexion, such as being burned by the sun, is to be understood as symbolic of her having crossed a sexual threshold without the benefit of marriage. (Vasvari 1999)

Identifying the brain regions that process facial color

There is a large body of research on the processing of facial color in the human mind, particularly on the brain regions involved. Thorstenson (2018) has reviewed the literature:

[...] there is considerable evidence suggesting that color is not merely an accessory of faces, but is rather a complex and crucial feature in facial processing. While classic  work  on  neural  processing  has  suggested  a  primary  cortical  area  responsible for face processing (FFA; Kanwisher, McDermott, & Chun, 1997) and a primary cortical area responsible for color processing (V4; McKeefry & Zeki, 1997), more recent work has revealed several areas in the temporal lobes specialized for face processing (Moeller, Freiwald, & Tsao, 2008; Tsao, Moeller, & Freiwald, 2008). Further, recent work has revealed consistent patterns of connected face and color selective cortical areas (Lafer-Sousa & Conway, 2013), possibly reflecting a shared overlap of visual processing between faces and color (Nakajima, Minami, Tanabe, Sadato, & Nakauchi, 2014; Stephen & Perrett, 2015). Additionally, the N170 component,  which  reflects  the  neural  processing  of  faces  in  event-related  potential  (ERP) studies, has been shown to respond to facial color information (Nakajima, Minami, & Nakauchi, 2012), but not to non-faces (Botzel & Grusser, 1989).

Thorstenson (2018) also reviews the possibilities for social signaling. Facial reddening is associated with anger and other intense emotions. Facial color can indicate certain disease states. Finally, there is a rise and fall in facial ruddiness and darkness over the menstrual cycle, with female facial color being lightest at ovulation.

Though providing a good review of the literature, Thorstenson should have mentioned three studies on female skin pigmentation over the menstrual cycle. McGuiness (1961) and Snell and Turner (1966) observed that facial skin darkens near the end of the cycle, particularly the peri-ocular skin of brunettes. Edwards and Duntley (1949) found that the buttocks visibly redden over the cycle, being lightest on the 13th day and darkest on the 25th day.

Conclusion

Today, skin color is seen through the lens of ethnic and racial conflict, yet this is not the sole meaning it has had for humans. For most of history and prehistory it was seen through a sexual lens, as a mark of masculinity or femininity.

This older meaning has received much less interest, even from academics. It is perhaps no coincidence that interest has come disproportionately from non-Western scholars like Hiroshi Wagatsuma, Kenichi Aoki, Mikiko Ashikari, and Aloke Kalla. In contrast, Western scholars, and Americans in particular, generally view the psychological meaning of skin color as a legacy of slavery.

References

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   

Alley, T.R. (2014[1986]). An ecological analysis of the protection of primate infants. In V. McCabe and G.J. Balzano (eds). Event Cognition: An Ecological Perspective. Routledge.

https://books.google.ca/books?id=YPTpAgAAQBAJ&printsec=frontcover&hl=fr&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false 

Aoki, K. (2002). Sexual selection as a cause of human skin colour variation: Darwin's hypothesis revisited. Annals of Human Biology 29(6): 589-608.

https://doi.org/10.1080/0301446021000019144   

Ashikari, M. (2005). Cultivating Japanese whiteness. The 'whitening' cosmetics boom and the Japanese identity. Journal of Material Culture 10(1):73-91.

https://doi.org/10.1177/1359183505050095    

Atzenhoffer, R. (2011). Les hommes préfèrent les blondes. Les lectrices aussi. Effet de psychologie, horizons idéologiques et valeurs morales des héroïnes dans l'œuvre romanesque de H. Courths-Mahler, Colloque national (CNRIUT), Villeneuve d'Ascq, 8-10 juin 2009,

http://cnriut09.univ-lille1.fr/articles/Articles/Fulltext/10a.pdf   

Baudouin, J.-Y., and R. Brochard. (2011). Gender-based prototype formation in face recognition. Journal of Experimental Psychology: Learning, Memory, and Cognition 37(4): 888-898.

http://dx.doi.org/10.1037/a0022963    

Bestelmeyer, P.E.G., B.C. Jones, L.M. DeBruine, A.C. Little, D.I. Perrett, A. Schneider, L.L.M. Welling, C.A. Conway. (2008). Sex-contingent face aftereffects depend on perceptual category rather than structural encoding. Cognition 107(1): 353-365.

https://doi.org/10.1016/j.cognition.2007.07.018    

Blaffer-Hrdy, S. (2000). Mother Nature: Maternal Instincts and How They Shape the Human Species. New York: Ballantine Books.

Booth, C. (1962). Some observations on behavior of Cercopithecus monkeys. Annals of the New York Academy of Sciences 102: 477-487.

https://doi.org/10.1111/j.1749-6632.1962.tb13654.x   

Bruce, V., and S. Langton. (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   

Capart, J. (1905). Primitive Art in Egypt. London: H. Grevel.

Carpenter, F. I. (1936). Puritans preferred blondes. The heroines of Melville and Hawthorne. New England Quarterly 9(2): 253-272.

https://doi.org/10.2307/360391   

Carrito, M.L., I.M.B. dos Santos, C.E. Lefevre, R.D. Whitehead, C.F. da Silva, and D.I. Perrett. (2016). The role of sexually dimorphic skin colour and shape in attractiveness of male faces. Evolution and Human Behavior 37(2): 125-33.

https://doi.org/10.1016/j.evolhumbehav.2015.09.006    

Dupuis-Roy, N., I. Fortin, D. Fiset, and F. Gosselin. (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    

Eaverly, M.A. (1999). Color and gender in ancient painting: A pan-Mediterranean approach. In N.L. Wicker and B. Arnold (eds). From the Ground Up: Beyond Gender Theory in Archaeology. Proceedings of the Fifth Gender and Archaeology Conference, University of Wisconsin-Milwaukee (pp. 5-10). Oxford (England): British Archaeological Reports.

Edwards, E.A., and S.Q. Duntley. (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 S.Q. Duntley. (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., J.B. Hamilton, S.Q. Duntley, and G. Hubert. (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    

Farah, M. J. (1996). Is face recognition 'special'? Evidence from neuropsychology. Behavioural

Brain Research 76(1-2): 181-189.
https://doi.org/10.1016/0166-4328(95)00198-0    

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. (2010). Femmes claires, hommes foncés. Les racines oubliées du colorisme. Quebec City: Les Presses de l'Université Laval, 202 p.

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    
Garza, R., R.R. Heredia, and A.B. Cieslicka. (2016). Male and female perception of physical attractiveness. An eye movement study. Evolutionary Psychology 14(1): 1-16. https://doi.org/10.1177/1474704916631614    

Gergen, K.J. (1967). The significance of skin color in human relations. Daedalus 96: 390-406.

http://www.jstor.org/stable/20027044  

Grande, R., E. Gutierrez, E. Latorre, and F. Arguelles. (1994). Physiological variations in the pigmentation of newborn infants. Human Biology 66(3): 495-507.
http://www.jstor.org/stable/41465000
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 S. Akamatsu. (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    

Jaquet, E., and G. Rhodes. (2008). Face aftereffects indicate dissociable, but not distinct, coding of male and female faces. Journal of Experimental Psychology: Human Perception and Performance 34(1): 101-112.

https://doi.org/10.1037/0096-1523.34.1.101    

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   

Kalla, A.K. (1973). Ageing and sex differences in human skin pigmentation. Zeitschrift für Morphologie und Anthropologie 65(1): 29-33.

http://www.jstor.org/stable/25756080   

Little, A.C., L.M. DeBruine, and B.C. Jones. (2005). Sex-contingent face after-effects suggest distinct neural populations code male and female faces. Proceedings of the Royal Society of London, Series B 272(1578): 2283-2287.

https://doi.org/10.1098/rspb.2005.3220    

Lorenz, K. 1971. Studies in Animal and Human Behaviour, vol. 2. London: Methuen & Co.

Maertens, J-T. (1978). Le dessein sur la peau. Essai d'anthropologie des inscriptions tégumentaires, Ritologiques I, Paris: Aubier Montaigne.

Manning, J.T., P.E. Bundred, and F.M. Mather. (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  

Mazess, R.B. (1967). Skin color in Bahamian Negroes. Human Biology 39(2): 145-154.

http://www.jstor.org/stable/41448835    

McGuiness, B.W. (1961). Skin pigmentation and the menstrual cycle. British Medical Journal 2(5251): 563-565.

http://www.jstor.org/stable/20354588   

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

Nestor, A., and M.J. Tarr. (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   

Pascalis, O., and D.J. Kelly. (2008). Face processing, in M. Haith and J. Benson (eds), Encyclopedia of Infant and Early Childhood Development. (pp. 471-478), Elsevier.

Post, P.W., A.N. Krauss, S. Waldman, and Peter A.M. Auld. (1976). Skin reflectance of newborn infants from 25 to 44 weeks gestational age. Human Biology 48(3): 541-557.

http://www.jstor.org/stable/41462904

Rupp, H.A., T.W. James, E.D. Ketterson, D.R. Sengelaub, E. Janssen, and J.R. Heiman. (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. Adams, N. Ambady, K. Nakayama, and S. Shimojo (eds.) The science of social vision. New York: Oxford.

Russell, R., B. Duchaine, and K. Nakayama. (2009). Super-recognizers: People with extraordinary face recognition ability. Psychonomic Bulletin & Review 16(2): 252-257.

https://doi.org/10.3758/PBR.16.2.252  

Russell, R. and P. Sinha. (2007). Real-world face recognition: The importance of surface reflectance properties. Perception 36(9): 1368-1374.

http://dx.doi.org/10.1068/p5779   

Segrave, K. (2005). Suntanning in 20th Century America. Jefferson (North Carolina): McFarland & Company.

Snell, R.S., and R. Turner. (1966). Skin pigmentation in relation to the menstrual cycle. The Journal of Investigative Dermatology 47(2): 147-155.

https://doi.org/10.1038/jid.1966.119  

Soustelle, J. (1970). The Daily Life of the Aztecs. Stanford, California: Stanford University Press.

Tarr, M.J., D. Kersten, Y. Cheng, and B. Rossion. (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., B. Rossion, and K. Doerschner. (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, http://journalofvision.org/2/7/598/   

https://doi.org/10.1167/2.7.598   

Tegner, E. (1992). Sex differences in skin pigmentation illustrated in art. The American Journal of Dermatopathology 14(3): 283-87.

https://doi.org/10.1097/00000372-199206000-00016  

Thorstenson, C.A. (2018). The social psychophysics of human face color: Review and recommendations. Social Cognition 36(2): 247-273.

https://doi.org/10.1521/soco.2018.36.2.247   
https://www.researchgate.net/publication/324145494_The_Social_Psychophysics_of_Human_Face_Color_Review_and_Recommendations   
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  

Vasvari, L.O. (1999). A comparative approach to European folk poetry and the erotic wedding motif, CLCWeb. Comparative Literature and Culture 1(4)

https://doi.org/10.7771/1481-4374.1050  

Wagatsuma, H. (1967). The social perception of skin color in Japan. Daedalus 96(2): 407-443.

http://www.jstor.org/stable/20027045   

Walentowitz, S. (2008). Des êtres à peaufiner. Variations de la coloration et de la pigmentation du nouveau-né, in J-P. Albert, B. Andrieu, P. Blanchard, G. Boëtsch, and D. Chevé (eds.) Coloris Corpus (pp. 113-120), Paris: CNRS Éditions, 2008.

Yip, A.W., and P. Sinha. (2002). Contribution of color to face recognition. Perception 31(8): 995-1003.

https://doi.org/10.1068/p3376  

Zahan, D. (1974). White, Red and Black: Colour Symbolism in Black Africa, in A. Portmann and R. Ritsema (eds.) The Realms of Colour, Eranos 41 (1972), 365-395, Leiden: Eranos.

Zhu, Q., Y. Song, S. Hu, X. Li, M. Tian, Z. Zhen, Q. Dong, N. Kanwisher, and J. Liu. (2009). Heritability of the specific cognitive ability of face perception. Current Biology 20(2): 137-142.

https://doi.org/10.1016/j.cub.2009.11.067   

A darker shade of pale

 

Subjects identified the left-hand image as a woman and the right-hand one as a man. Yet the two images differ only in skin tone. Study by Richard Russell, Sinha Laboratory for Vision Research, MIT.

 

Skin color differs by sex: women are fairer and men browner and ruddier. Women also exhibit a greater contrast in luminosity between their facial skin and their lip and eye areas. These differences arise from differing concentrations of three skin pigments: melanin (brown); hemoglobin (red); and carotene (yellow). The cause is ultimately hormonal, as shown by studies on castrated and ovariectomized adults, on boys and girls during puberty, and on digit ratios (Edwards and Duntley, 1939; Edwards and Duntley, 1949; Edwards et al., 1941; Frost, 2010; Kalla and Tiwari, 1970; Manning et al., 2004; Mesa, 1983; Omoto,1965; Porcheron et al., 2013). Women are fairer than men in all human populations. The difference is greatest in people of medium color and least in very dark- or very fair-skinned people, apparently because of "floor" or "ceiling" effects (Frost, 2007). 

This sex difference is used by the human mind for sex recognition. In fact, it's more important for this purpose than other visual cues, like face shape. When subjects are shown an image of a human face, they can tell whether it is male or female even if blurred and differing only in hue and luminosity. Hue provides a "fast channel" for sex recognition. If the facial image is too far away or the lighting too dim, the mind switches to the "slow channel" and relies on luminosity (Bruce and Langton, 1994; Dupuis-Roy et al., 2009; Frost, 2011; Hill et al., 1995; Russell and Sinha, 2007; Russell et al., 2006; Tarr et al., 2001; Tarr et al., 2002).

Age differences

Skin color also differs by age. It can be used to distinguish younger from older women, since the contrast in luminosity between facial skin and the lip/eye areas decreases with age (Porcheron et al., 2013). It can also be used to recognize infants. All humans are born with very little melanin, and the resulting pinkish-white skin is often remarked upon in different cultures.

This is especially so where adults are normally dark-skinned, in striking contrast to newborns. In Kenya, the latter are often called mzungu ('European' in Swahili), and a new mother may ask her neighbors to come and see her mzungu (Walentowitz, 2008). Among the Tuareg, children are said to be whitened by the freshness and moisture of the womb (Walentowitz, 2008). The situation in other African peoples is summarized by a French anthropologist: "There is a rather widespread concept in Black Africa, according to which human beings, before 'coming' into this world, dwell in heaven, where they are white. For, heaven itself is white and all the beings dwelling there are also white. Therefore the whiter a child is at birth, the more splendid it is" (Zahan, 1974, p. 385). A Belgian anthropologist makes the same point: "black is thus the color of maturity [...] White on the other hand is a sign of the before-life and the after-life: the African newborn is light-skinned and the color of mourning is white kaolin" (Maertens, 1978, p. 41). 

This infant/adult difference is evolutionarily old, being present in nonhuman primates. In langurs, baboons, and macaques, the newborn's skin is pink while the adult's is black. This visual cue not only helps adults to locate a wayward infant but also seems to induce a desire to defend and provide care (Jay, 1962). Humans may respond similarly to the lighter color of infants and women. This would be consistent with a tendency by the adult female body to mimic the newborn body in other ways: face shape; pitch of voice; amount of body hair; texture and pliability of the skin; etc. Over time, women may have come to resemble this 'infant schema' because it is the one that can best reduce aggressiveness in a male partner and induce him to assume a provider role.

 

The sun-tanning fad: An aesthetic revolution

The sex-specific aspects of skin color have influenced the development of cosmetics in many cultures. Even in ancient times, women would use makeup to increase the natural contrast in luminosity between their facial skin and their lip/eye areas (Russell, 2009; Russell, 2010). They would also make their naturally fair complexion even fairer by avoiding the sun and applying white powders or bleaching agents.

This feminine aesthetic changed radically in the 1920s with the sudden popularity of sun-tanning throughout the Western world, initially as a health fad. Tanned skin then entered women's fashion and became part of the flapper image, along with bobbed hair, broad shoulders, a relatively flat chest, narrow hips, and long legs. This fashion image was intended to be hermaphroditic, the aim being to energize the erotic appeal of the female body by masculinizing some of its key features (Bard, 1998; Segrave, 2005). 

Has the tanning fad un-gendered skin color? Not wholly, to judge by the above studies on sex recognition. There still seems to be a tendency to prefer a lighter skin tone for women than for men. This was the conclusion of a recent study on how people perceive two skin pigments: melanin (brown) and carotene (yellow). When shown facial images with varying concentrations of melanin and carotene, the subjects had a greater preference for carotene than for melanin. This preference was stronger for female faces than for male faces, irrespective of the observer's sex. Nonetheless, for both male and female faces, the preferred skin color was much darker than it would have been a century ago (Lefevre and Perrett, 2014).

Again, this aesthetic norm has darkened only in the Western world. The tanned look had some popularity among Japanese women in the postwar era up to the 1970s, but it has since gone out of fashion (Ashikari, 2005). It never did catch on elsewhere in Asia (Li et al., 2008). In North America and Europe, the tanned look seems much more persistent, and this persistence suggests that it is locked into place by something else in our cultural environment.

Such as ...? One factor may be the conscious effort to promote images of dark-skinned people in advertising and, more generally, in popular culture. Another factor may be a half-conscious desire in popular culture for more aggressive, "harder" forms of eroticism. This is something that fair skin is less effective at delivering, having been originally part of the infant schema and thus less conducive to that kind of emotional response.

 

References

Ashikari, M. (2005). Cultivating Japanese whiteness. The 'whitening' cosmetics boom and the Japanese identity, Journal of Material Culture, 10, 73-91. 

Bard, C. (1998). Les Garçonnes. Modes et fantasmes des Années folles, Flammarion, Paris. 

Bruce, V., and S. Langton. (1994). The use of pigmentation and shading information in recognising the sex and identities of faces, Perception, 23(7), 803-822.

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

http://journalofvision.org/9/2/10/

Edwards, E.A. and S.Q. Duntley. (1949). Cutaneous vascular changes in women in reference to the menstrual cycle and ovariectomy, American Journal of Obstetrics and Gynecology, 57, 501-509.

Edwards, E.A. and S.Q. Duntley. (1939).The pigments and color of living human skin, American Journal of Anatomy, 65, 1-33.

Edwards, E.A., J.B. Hamilton, S.Q. Duntley, and G. Hubert. (1941). Cutaneous vascular and pigmentary changes in castrate and eunuchoid men, Endocrinology, 28, 119-128. 

Frost, P. (2011). Hue and luminosity of human skin: a visual cue for gender recognition and other mental tasks, Human Ethology Bulletin,

http://www.researchgate.net/publication/256296588_Hue_and_luminosity_of_human_skin_a_visual_cue_for_gender_recognition_and_other_mental_tasks/file/72e7e5223eb2c3eb3b.pdf

Frost, P. (2010). Femmes claires, hommes foncés. Les racines oubliées du colorisme, Québec: Les Presses de l'Université Laval, 202 p.

Frost, P. (2007). Comment on Human skin-color sexual dimorphism: A test of the sexual selection hypothesis, American Journal of Physical Anthropology, 133, 779-781.

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

Jay, P.C. (1962). Aspects of maternal behavior among langurs, Annals of the New York Academy of Sciences, 102, 468-476.

http://onlinelibrary.wiley.com/doi/10.1111/j.1749-6632.1962.tb13653.x/abstract

Kalla, A.K. and S.C. Tiwari. (1970). Sex differences in skin colour in man, Acta Geneticae Medicae et Gemellologiae, 19, 472-476. 

Lefevre, C.E. and D.I. Perrrett. (2014). Fruit over sunbed: Carotenoid skin colouration is found more attractive than melanin colouration, The Quarterly Journal of Experimental Psychology,

http://www.tandfonline.com/doi/full/10.1080/17470218.2014.944194#tabModulehttp://www.tandfonline.com/doi/full/10.1080/17470218.2014.944194#tabModule

Li, E.P.H., H.J. Min, R.W. Belk, J. Kimura, and S. Bahl. (2008). Skin lightening and beauty in four Asian cultures, Advances in Consumer Research, 35, 444-449.

http://www.acrwebsite.org/volumes/v35/naacr_vol35_273.pdf

Maertens, J-T. (1978). Le dessein sur la peau. Essai d'anthropologie des inscriptions tégumentaires, Ritologiques I, Paris: Aubier Montaigne. 

Manning, J.T., P.E. Bundred, and F.M. Mather. (2004). Second to fourth digit ratio, sexual selection, and skin colour, Evolution and Human Behavior, 25, 38-50.

http://www.ehbonline.org/article/S1090-5138(03)00082-5/abstract 

Mesa, M.S. (1983). Analyse de la variabilité de la pigmentation de la peau durant la croissance, Bulletin et mémoires de la Société d'Anthropologie de Paris, t. 10 series 13, 49-60.

http://www.persee.fr/web/revues/home/prescript/article/bmsap_0037-8984_1983_num_10_1_3882 

Omoto, K. (1965). Measurements of skin reflectance in a Japanese twin sample, Journal of the Anthropological Society of Nippon (Jinruigaku Zassi), 73, 115-122.

http://ci.nii.ac.jp/naid/130003726811/http://ci.nii.ac.jp/naid/130003726811/ 

Porcheron, A., E. Mauger, and R. Russell (2013). Aspects of facial contrast decrease with age and are cues for age perception, PLoS ONE 8(3): e57985

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0057985 

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

http://public.gettysburg.edu/~rrussell/Russell_SocialVision_cosmetics_chapter.pdf 

Russell, R. (2009). A sex difference in facial contrast and its exaggeration by cosmetics, Perception, 38, 1211-1219

http://public.gettysburg.edu/~rrussell/Russell_2009.pdf

Russell, R. (2003). Sex, beauty, and the relative luminance of facial features, Perception, 32, 1093-1107.

Russell, R. and P. Sinha. (2007). Real-world face recognition: The importance of surface reflectance properties, Perception, 36, 1368-1374.

Russell, R., P. Sinha, I. Biederman, and M. Nederhouser. (2006). Is pigmentation important for face recognition? Evidence from contrast negation, Perception, 35, 749-759.

Segrave, K. (2005). Suntanning in 20th Century America, Jefferson (North Carolina), McFarland & Co. 

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

http://journalofvision.org/1/3/337/

Walentowitz, S. (2008). Des êtres à peaufiner. Variations de la coloration et de la pigmentation du nouveau-né, in J-P. Albert, B. Andrieu, P. Blanchard, G. Boëtsch, and D. Chevé (eds.), Coloris Corpus, (pp. 113-120), Paris: CNRS Éditions, 2008.

Zahan, D. (1974). White, Red and Black: Colour Symbolism in Black Africa, in A. Portmann and R. Ritsema (eds.) The Realms of Colour, Eranos 41 (1972), 365-395, Leiden: Eranos.

How modular is intelligence?

Great at reading or recognizing faces? You might not do so well on an IQ test. Source: Histoire naturelle générale et particulière avec la Description du Cabinet du Roy (1749) (Wikicommons)

 

The English psychologist Charles Spearman was the first to argue that a single factor, called "g," explains most of the variability in human intelligence. When observing the performance of children at school, he noticed that a child who did well in math would also do well in geography or Latin. There seemed to be a general factor that facilitates almost any kind of mental task.

Spearman did, however, acknowledge the existence of other factors that seem more task-specific:

[...] all branches of intellectual activity have in common one fundamental function (or group of functions), whereas the remaining or specific elements of the activity seem in every case to be wholly different from that in all the others. (Spearman, 1904, p. 284) 

That is where things stood for over a century. In recent years, however, we’ve begun to identify the actual genes that contribute to intelligence. These genes are very numerous, numbering perhaps in the thousands, with each one exerting only a small effect. Many act broadly on intelligence in general and may correspond to the g factor, which seems to be a widespread property of neural tissue, perhaps cortical thickness or the integrity of white matter in the brain. Other genes act more narrowly on specific mental tasks. The ability to recognize faces, for instance, seems to have no relation at all to general intelligence. You can be great at recognizing faces while being as dumb as rocks (Zhu et al., 2009).

One way to locate these genes is through genome-wide association studies. We look at the various alleles of genes whose locations are already known, typically SNPs (single nucleotide polymorphisms), and see whether this source of variability correlates with variability in a mental trait. If we find a significant correlation, the genes for that trait must be nearby. The same kind of study can also show us how narrowly or broadly these genes act. Do they merely influence intelligence in general? Or do they provide more specific instructions? Such as how to recognize certain objects or how to react to them?

A genome-wide association study has recently shed light on various mental traits. In most cases, a common factor seems to explain about half of the genetic variability. This common factor is weakest for emotion identification, i.e., the ability to identify the emotions of other people by their facial expressions. Emotion identification actually correlates negatively with nonverbal reasoning (-0.25) and only weakly with verbal memory (0.17) and spatial reasoning (0.26). The highest correlation is with reading (0.40) and language reasoning. (0.45). Reading and language reasoning are highly intercorrelated, perhaps because they share the same mental module (Robinson et al., 2014).

This partial modularity has been confirmed by a recent twin study on reading and math ability. If we look at the genetic component of either reading or math ability, at least 10% and probably half affects performance on both tasks. Conversely, the other half is specific to either one or the other (Davis et al., 2014).

 

An evolutionary mystery?

But how can reading ability have a specific genetic basis if people began to read only in historic times? Indeed, history is said to begin with the first written documents. Surely humans weren't still evolving at that point?

To ask the question is to answer it. Not only were they still evolving, they were actually doing so at a faster pace than their prehistoric ancestors. Humans have undergone much more genetic change over the past 10,000 years than over the previous 100,000 (Hawks et al., 2007). This is a difficult fact to swallow, let alone digest, but we must learn to accept it and all of its implications.

The new findings on reading ability are consistent with other ones. The human brain has a special region, called the Visual Word Form Area, that is used to recognize written words and letters. If it is damaged, your reading ability will suffer but not your recognition of objects, names, faces, or general language abilities. There will be some improvement over the next six months, but reading will still take twice as long as it had previously. This brain region varies in size and organization from one individual to another and from one human population to another, being differently organized in Chinese people than in Europeans (Frost, 2014; Gaillard et al, 2006; Glezer and Riesenhuber, 2013; Levy et al., 2013; Liu et al., 2008).

Genome-wide association studies may help us pinpoint the actual genes responsible for the Visual Word Form Area. In fact, we may have already found one: ASPM. This gene influences brain growth in other primates and has evolved in humans right up into historic times. Its latest allele arose about 6000 years ago in the Middle East and proliferated until it reached incidences of 37-52% in Middle Easterners, 38-50% in Europeans, and 0-25% in East Asians. Despite its apparent selective advantage, this allele does not improve performance on IQ tests (Mekel-Bobrov et al.,2007; Rushton et al., 2007). It is nonetheless associated with larger brain size in humans (Montgomery and Mundy, 2010).

Its Middle Eastern origin some 6000 years ago suggests this allele may have owed its success to the invention of writing. Most people had trouble reading, writing, and copying lengthy texts in ancient times, when characters were written continuously with little or no punctuation. There was an acute need for scribes who could excel at this task, and such people were rewarded with reproductive success (Frost, 2008; Frost, 2011).

 

Conclusion

Human intelligence is modular to varying degrees, and much of this modularity seems to have arisen during historic times. It is a product of humans adapting not only to their physical environments but also to their more rapidly evolving cultural environments.

While there is such a thing as general intelligence, it seems to be only half of the picture. Two people may have the same IQ and yet differ significantly in various mental abilities. There may also be trade-offs between general intelligence and more specific mental tasks. If you're great at abstract reasoning, you may be lousy at decoding facial expressions. This may be because the two abilities compete with each other for limited mental resources. Or it may be that selection for abstract reasoning has occurred in an environment where people can trust each other and have no need to scrutinize facial expressions for signs of lying ... or imminent physical assault. 

The same applies to human populations. Two populations may have the same mean IQ, and yet differ statistically over a large number of mental and behavioral traits. Although these differences may be scarcely noticeable if we compare two individuals taken at random from each population, their accumulative effect over many thousands of individuals can steer one population along one path of cultural evolution and the other along another. Furthermore, two populations may arrive at a similar outcome via different paths of cultural evolution and via different mental and behavioral packages. Europeans and East Asians have both reached an advanced level of societal development, but this similar outcome has been achieved in East Asian societies largely through external mediation of rule enforcement (e.g., shaming, peer pressure, family discipline) and in European ones mainly through internal means of control (e.g., guilt, empathy).

 

References

 

Davis, O.S.P., G. Band, M. Pirinen, C.M.A. Haworth, E.L. Meaburn, Y. Kovas, N. Harlaar, et al. (2014). The correlation between reading and mathematics ability at age twelve has a substantial genetic component, Nature Communications, 5

http://www.nature.com/ncomms/2014/140708/ncomms5204/full/ncomms5204.html 

Frost, P. (2008). The spread of alphabetical writing may have favored the latest variant of the ASPM gene, Medical Hypotheses, 70, 17-20.

http://www.sciencedirect.com/science/article/pii/S0306987707003234

Frost, P. (2011). Human nature or human natures? Futures, 43, 740-748. http://dx.doi.org/10.1016/j.futures.2011.05.017  

Frost, P. (2014). The paradox of the Visual Word Form Area, March 1, Evo and Proud

http://evoandproud.blogspot.ca/2014/03/the-paradox-of-visual-word-form-area.html 

Gaillard, R., Naccache, L., P. Pinel, S. Clémenceau, E. Volle, D. Hasboun, S. Dupont, M. Baulac, S. Dehaene, C. Adam, and L. Cohen. (2006). Direct intracranial, fMRI, and lesion evidence for the causal role of left inferotemporal cortex in reading, Neuron, 50, 191-204.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.76.7620&rep=rep1&type=pdf  

Glezer, L.S. and M. Riesenhuber. (2013). Individual variability in location impacts orthographic selectivity in the "Visual Word Form Area", The Journal of Neuroscience, 33(27), 11221-11226.

http://www.jneurosci.org/content/33/27/11221.full 

Hawks, J., E.T. Wang, G.M. Cochran, H.C. Harpending, and R.K. Moyzis. (2007). Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences (USA), 104, 20753-20758.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2410101/ 

Levy, J., J.R Vidal, R. Oostenveld, I. FitzPatrick, J-F. Démonet, and P. Fries. (2013). Alpha-band suppression in the Visual Word Form Area as a functional bottleneck to consciousness, NeuroImage, 78C, 33-45.

http://hal.inria.fr/docs/00/81/96/67/PDF/Levy_et_al.pdf 

Liu, C., W-T. Zhang, Y-Y Tang, X-Q. Mai, H-C. Chen, T. Tardif, and Y-J. Luo. (2008). The visual word form area: evidence from an fMRI study of implicit processing of Chinese characters, NeuroImage, 40, 1350-1361.

http://www.yi-yuan.net/english/PAPERS/PAPERS_2008/2008_The-Visual-Word-Form-Area-Evidence.pdf  

Mekel-Bobrov, N., Posthuma, D., Gilbert, S. L., Lind, P., Gosso, M. F., Luciano, M., et al. (2007). The ongoing adaptive evolution of ASPM and Microcephalin is not explained by increased intelligence, Human Molecular Genetics, 16, 600-608.

http://psych.colorado.edu/~carey/pdfFiles/ASPMMicrocephalin_Lahn.pdf  

Montgomery, S. H., and N.I. Mundy. (2010). Brain evolution: Microcephaly genes weigh in, Current Biology, 20, R244-R246.

http://www.sciencedirect.com/science/article/pii/S0960982210000862  

Robinson, E.B., A. Kirby, K. Ruparel, J. Yang, L. McGrath, V. Anttila, B.M. Neale, K. Merikangas, T. Lehner, P.M.A. Sleiman, M.J. Daly, R. Gur, R. Gur and H. Hakonarson. (2014). The genetic architecture of pediatric cognitive abilities in the Philadelphia Neurodevelopmental Cohort, Molecular Psychiatry, published online July 15

http://www.nature.com/mp/journal/vaop/ncurrent/full/mp201465a.html

Rushton, J. P., Vernon, P. A., and Bons, T. A. (2007). No evidence that polymorphisms of brain regulator genes Microcephalin and ASPM are associated with general mental ability, head circumference or altruism, Biology Letters, 3, 157-160.

http://semantico-scolaris.com/media/data/Luxid/Biol_Lett_2007_Apr_22_3(2)_157-160/rsbl20060586.pdf

Spearman, C. (1904). "General intelligence," objectively determined and measured, The American Journal of Psychology, 15, 201-292.

http://www.jstor.org/stable/1412107

Zhu, Q., Song, Y., Hu, S., Li, X., Tian, M., Zhen, Z., Dong, Q., Kanwisher, N. and Liu, J. (2009). Heritability of the specific cognitive ability of face perception, Current Biology, 20, 137-142.

http://web.mit.edu/bcs/nklab/media/pdfs/Zhu_et_al_Heritability.pdf