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.

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