Recent evolution of hair, eye and skin color in Europe

Europeans acquired their current appearance long after their ancestors entered Europe. The changes occurred relatively fast, and went further in women than in men.

Written by Peter Frost.

Europeans have a surprising variety of hair and eye colors. Their hair colors are produced by alleles at over 200 loci and their eye colors by alleles at over 124 (Morgan et al., 2018; Simcoe et al., 2021). These alleles went from being nonexistent to their current high prevalence within a relatively short span of time, certainly less than the forty thousand years of Homo sapiens in Europe. Only a very strong kind of selection could have caused so many alleles to become so common so fast (Frost, 2006; Frost, 2022).

That selection is often attributed to lack of vitamin D at higher latitudes. As humans spread out of Africa and into Europe, where sunlight is weaker, selection would have favored lighter skin to allow in more UVB and maintain enough synthesis of vitamin D. Meanwhile, hair and eye color would have changed as a side-effect.

That explanation is hard to reconcile with some aspects of hair, eye, and skin color among Europeans:

1. The genetic linkages are weak between skin color, hair color and eye color. In fact, the genes are different in each case. European skin became white through new alleles at SLC45A2, SLC24A5, and TYRP1; hair color diversified mainly through new alleles at MC1R; and eye color diversified mainly through new alleles in the HERC2–OCA2 region. This is why pale skin often coexists with dark hair and dark eyes. Therefore, selection for lighter skin should not have a strong effect on hair and eye color.

2. European hair and eye colors are due to an unusually large number of alleles. If the selection had been only for lighter skin, and if the other visible changes were due only to an overall reduction in melanin, European hair would have simply become less black and European eyes less brown. We still need to explain the proliferation of so many new alleles that produce such a wide range of hues.

3. European hair and eye colors are brighter and “purer.” In other words, they reflect more light within thinner slices of the visible spectrum than the original black and brown. Pure, bright colors are unusual in nature and typically exist to attract attention, for instance to help a flower get pollinated or to help an animal find a mate.

4. European hair and eye colors are more frequent in women. Women are much more likely than men to have red or blond hair, and three to five times less likely to have black hair. This natural sex difference has been confirmed by controlled studies and is especially large for red hair (Hysi et al., 2018; Shekar et al., 2008). Among Czechs, 19% of women and 11% of men have the highest gradation of hair redness (Frost et al., 2017). The less frequent hair colors thus occur more often in women, and the more frequent ones less often. Consequently, the various hair colors are more evenly distributed among women than among men.

The various eye colors are likewise more evenly distributed among women. This does not mean that the colors specific to Europeans are always more frequent in women. Blue eyes are actually more frequent in men, probably because blue was the first of the new eye colors and only later differentiated to produce green and hazel – which are indeed more frequent in women (Frost et al., 2017; Frost, 2022, pp. 9-10, 13).

Population frequencies of eye colors, by sex (Frost et al., 2017).

European hair and eye colors seem to be facilitated by estrogen

This sex difference apparently has a hormonal cause. Specifically, the female hormone estrogen seems to favor the expression of non-black hair and non-brown eyes during fetal development.

An estrogenic effect is highly likely for red hair, which is the hair color that differs most in frequency between men and women. According to a health survey of 7,000 Czech participants, male redheads are as healthy as other men, doing better on average in three categories and worse in three. Female redheads, however, do worse on average than other women in ten categories and better in only three. They are especially prone to four types of cancer: colorectal, cervical, uterine, and ovarian – three of which are estrogen-dependent. Being both female and red-haired seems to maximize the risk of developing an estrogen-dependent disease, probably because these two risk factors are each associated with higher estrogen levels in a developing fetus. Together, they are associated with the highest estrogen levels (Frost et al., 2017).

A higher level of fetal estrogenization may explain why several studies have found an association between blue eyes and certain feminine traits. Note: although blue eyes are actually more frequent in men than in women, these studies used a broad definition of “blue” that included green and hazel (which are more frequent in women).

• Blue-eyed boys tend to be shy. This is the “little boy blue” effect. A study of preschoolers found more social wariness in blue-eyed boys than in brown-eyed boys. The difference was greatest at the extremes of wariness. Among the very inhibited boys, 13 out of 14 were blue-eyed. Among the very uninhibited, only 4 out of 10 were. There was no such relationship among the girls, whose eyes were blue in 5 out of 9 among the very inhibited and in 6 out of 11 among the very uninhibited (Coplan et al., 1988).

• Blue-eyed women tend to have narrower shoulders and higher hip-to-waist ratios. A Latvian study found small but significant correlations between female eye color and certain sexually dimorphic features. Shoulders were narrower and hip-to-waist ratios higher in blue-eyed women than in brown-eyed women (Kažoka and Vētra, 2011).

• Blue-eyed men tend to have more feminine faces. This was an unintended finding of two Czech studies whose participants were asked to rate male and female facial photos. Initially, the brown-eyed male faces were rated as more dominant than the blue-eyed male faces. When, as a control, the brown-eyed faces were photoshopped to make them blue-eyed, they were still rated as more dominant. On careful examination, the originally brown-eyed faces were found to be more masculine with broader and more massive chins, broader mouths, larger noses, larger eyebrows, and closer-set eyes. The originally blue-eyed faces had smaller and sharper chins, narrower mouths, smaller noses, and greater distance between the eyes.

Blue eyes were associated with a more feminine facial shape only when the faces were male, just as blue eyes were associated with shyness only in boys. Perhaps natural selection has ensured that female fetuses always receive enough estrogen for their physical and behavioral development. Male fetuses may be exposed to a range of estrogen levels with more variable effects (Kleisner et al., 2010; Kleisner et al., 2013).

Were brown eyes associated with a different facial shape in this study because some of the brown-eyed men were partly Jewish or Roma and had a more Mediterranean appearance? In that case, facial shape would have been more variable in the brown-eyed men. It was not. This explanation also fails to explain the effect of gender: why were blue eyes associated with facial feminization in men but not in women?

Averaged faces of blue-eyed men (left) and brown-eyed men (right), Czech population (Kleisner et al., 2010).

Sexual selection?

In sum, European hair and eye colors do not seem to be a side-effect of selection for lighter skin. They are unusually diverse, being due to a large number of alleles that arose at different loci over a relatively short span of time. They are also brighter and purer than the original black and brown. With the exception of blue eye color (if defined to exclude green and hazel), they are more frequent in women, apparently because estrogen helps them appear during fetal development.

If these hair and eye colors are not a side-effect of selection, could they be a direct effect? If so, who or what was doing the selecting and for what reason? Natural selection seems unlikely because it tends to favor a drab, nondescript look to minimize detection by predators. In contrast, sexual selection favors a colorful appearance to maximize detection by the opposite sex. This is especially true if your sex outnumbers the other in the mating market. The other sex can pick and choose, and their mate choice will be influenced by eye-catching characteristics, such as bright and pure colors.

European hair and eye colors get attention not only through their brightness and purity but also through their diversity – they come in many hues. Sexual selection is known to create color polymorphisms as a means to maximize the “novelty effect.” A color can get attention simply by being rare. When an attractive color becomes more frequent in a population through generations of sexual selection, it loses some of its novelty and, hence, some of its attractiveness. The pressure of selection then shifts to less frequent colors, including those that have recently appeared through mutation. Thus, over successive generations, the population will accumulate more and more color variants.

Finally, European hair and eye colors are eye-catching because they are located on or near the face, which is the focus of visual attention. We look at faces because facial expressions and eye movements are a rich source of information on a person’s emotions, intentions and preferences (Min et al., 2017).

The evidence for sexual selection is certainly suggestive. What are the chances that two color polymorphisms – one for the hair and one for the eyes – would arise independently at different genes, within the same geographic area, during the same time period, and on the same region of the body?

European skin color

Let’s turn to the skin color of Europeans. Could sexual selection explain their albino-like skin?

Again, the counter-argument is that skin became white at high European latitudes to maintain sufficient production of vitamin D. But why, then, did it fail to whiten to the same degree at similar latitudes in Asia and North America? Even in Europe, humans remained brown-skinned long after they came to that continent some 40,000 years ago. Three research teams have estimated that white skin became prevalent in Europe no earlier than 19,000 years ago (Canfield et al., 2014; Beleza et al., 2013; Norton and Hammer, 2007). In some regions, Europeans remained brown-skinned until almost the dawn of history, as shown by DNA dated to 8,000 years ago from Luxembourg, 7,000 years ago from Spain, and 5,000-4,000 years ago from England (Brace et al., 2019; Lazaridis et al., 2014; Olalde et al., 2014).

There is an alternative version of the vitamin D argument: Europeans became white when they gave up fishing and sealing for farming, and thus lost a major dietary source of vitamin D. However, two ancient DNA studies have shown a high prevalence of white skin in Scandinavians 9,500 to 6,000 years ago and in Baltic peoples 7,460 to 5,360 years ago (Günther et al., 2018; Mittnik et al., 2018). That was long before farming, when fishing and sealing still provided much of the diet.

So what made Europeans so white? Probably the same selection that made their hair and eyes so diversely colored. Unlike their hair and eyes, however, their skin did not acquire a variety of colors. It just became pale. The reason may be that sexual selection was guided by a pre-existing sexual dimorphism, that is, male skin is browner and ruddier than female skin in all human populations (Edwards and Duntley, 1939; Edwards and Duntley, 1949; Edwards et al., 1941; Frost, 2023; Manning et al., 2004). Lighter-skinned women are thus seen as more feminine in traditional cultures and preferred as mates (van den Berghe and Frost, 1986). When sexual selection is sufficiently strong, it should drain the gene pool of alleles for dark skin.

Ultimately, women have a lighter skin for the same reason they have a smaller nose and chin, a smoother, more pliable skin, and a higher pitch of voice. These are all visual, tactile, and auditory cues that originally identified the human infant to an adult observer, who would respond by being less aggressive and more willing to provide care and nurturance. By mimicking those cues, women could strengthen the pair-bond and better ensure male provisioning (Frost, 2010, pp. 134-135; Frost, 2011; Lorenz, 1971, pp. 154-164).

The lighter skin of infants is especially noticeable in societies where adults are much darker. When, for an ethnographic study, Zambian girls were asked to describe how Africans look, they typically answered: “At birth African children are born like Europeans, but after a few months the color changes to the color of an African” (Powdermaker, 1956).

Evolution of the new European phenotype across time and space

Ancestral Europeans underwent a radical change in their outward appearance within a limited span of time and space – essentially ten to twenty thousand years ago during the last ice age on a vast expanse of steppe-tundra stretching from the Baltic to central Siberia.

Despite high bioproductivity, that environment provided humans with only one food source: meat from wandering herds of reindeer and other game (Hoffecker, 2002, pp. 8, 178, 193-194, 237). This dependence on meat had two consequences:

• A high male death rate. Men had to hunt over long distances of cold, unstable terrain that offered no alternative food sources. There was thus a high risk of death from starvation and other hazards of hunting.

• A low polygyny rate. Only the ablest hunters could provide for more than one woman and her children, since the latter could not provide for themselves. Women had no food autonomy.

As a result, the mating market had a glut of women. There was intense rivalry among them for male attention, and strong selection for eye-catching features. Such features became more frequent with succeeding generations, altering not only how women looked but also how men looked, thereby creating a radically new appearance.

The height of the last ice age brought harsh climatic conditions and depopulation. Chances of survival were better for the new phenotype at the European end of the steppe-tundra, where the climate was milder and wetter, and the human population much larger. At the Asian end, the human population was smaller and at greater risk of extinction. Nonetheless, the new phenotype did survive in parts of northern Asia, even into historic times. A site in south-central Siberia, dated to the fourth century AD, has yielded the remains of individuals who, according to genetic analysis, had blue or green eyes, blond, red, or light brown hair, and fair skin (Bouakaze et al., 2009). Indeed, old Chinese records describe south Siberian peoples with “green eyes” and “red hair” (Keane, 1886, p. 703).

Although that phenotype eventually disappeared from northern Asia, it persisted in the north and east of Europe and would even spread across the entire continent during post-glacial times, between ten and four thousand years ago. It was thus on the eve of recorded history that all Europeans acquired their white skin and diverse hair and eye colors, like a cast of actors being hastily made up and rushed onto stage moments before curtain time (Frost, 2022a).

Evolution of the new European phenotype: 45,000 - 4,000 BP.

Peter Frost has a PhD in anthropology from Université Laval. His main research interest is the role of sexual selection in shaping highly visible human traits, notably skin color, hair color and eye color. Other research interests include gene-culture coevolution. Find his newsletter here.

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