The puzzle of European hair, eye, and skin color

 

Mary Magdalene, Frederick Sandys (1829-1904). Is the physical appearance of Europeans solely or even mainly an adaptation to climate?

 

The Russian online magazine Kultura VRN has published an article I wrote on the "puzzle of European hair, eye, and skin color." The following is the original English text.

 

Most humans have black hair, brown eyes, and brown skin. Europeans are different: their hair is also brown, flaxen, golden, or red, their eyes also blue, gray, hazel, or green, and their skin pale, almost like an albino's. This is particularly the case in northern and eastern Europeans. 

How did this color scheme come about? Perhaps the same genes that lighten skin pigmentation also affect hair and eye pigmentation. Yet the genes are different in each case. Our skin became white mainly through the replacement of one allele by another at three separate genes. Our hair acquired a diverse palette of colors through a proliferation of new alleles at another gene. Our eyes acquired a similar palette through similar changes at yet another gene.

This color scheme is puzzling in another way: it is stronger in women than in men. Women are naturally more variable than men in hair color, redheads in particular being more common. They are likewise more variable in eye color in those populations where blue eyes are common. Finally, throughout the world, women are fairer-skinned than men, as a result of cutaneous changes at puberty.

While women are more diversely colored in their hair and eyes, this greater diversity has a different cause in each case. In the case of hair color, women have more of the intermediate hues because the darkest hue (black) is less easily expressed. In the case of eye color, women have more of the intermediate hues because the lightest hue (blue) is less easily expressed.

If hair color and eye color diversified in ways that differ physiologically but are similar visually, then the common purpose of this diversity must be visual. Furthermore, in both cases, this diversity concerns visible features on or near the face—the focus of visual attention.

Sexual selection?

Why would a facial feature become more colorful in one sex than in the other? The likeliest reason is sexual selection, which occurs when one sex has to compete for the attention of the other. This kind of selection favors eye-catching colors that are either bright or novel.

Bright colors stay in memory longer. If we look at the hair and eye colors that arose in Europe, we see that they are brighter than the human norm of black hair and brown eyes. Hair is carrot red but not beet red. Eyes are sky blue but not navy blue.

Novel colors hold attention longer. Attraction to novelty may explain how the European palette of hair and eye colors came into being. First, a new color would appear by mutation and be initially rare and novel. Second, its novelty would attract attention and increase one's chances of mating, with the result that the color would become more common in succeeding generations. Third, attention would now shift toward rarer and more novel colors that had recently appeared by mutation. All in all, it was this fascination with novelty that caused the number of hair and eye colors to increase steadily over time, once sexual selection had become strong enough.

This novelty effect appears in a study on male preferences for female hair color. Men were shown a series of photos of attractive blondes and brunettes, and they were asked to choose the one they most wanted to marry. It turned out that the scarcer the brunettes were in the series, the likelier any one brunette would be chosen. Another study likewise found that Maxim cover girls are much more often light blonde or dark brown than the usual dark blonde or light brown of real life.

A preference will become a choice only if one has a choice. This is the principle of sexual selection: one sex is in a better position to choose than the other. In most mammalian species, females are in a better position because they can choose among a larger number of males on the mate market. This is because the latter are almost always available for mating, whereas females are unavailable during pregnancy and the period of infant care. Males thus tend to be polygamous.

In early human societies that lived from hunting and gathering, the incidence of polygamy varied with latitude. It was highest in the tropics, where a woman could gather food year-round and feed herself and her children with little male assistance. This self-reliance made it easier for her mate to look for another woman.

Beyond the tropics, women were less self-reliant, particularly during winter when they could no longer gather food and depended on meat from their spouses. This dependence increased with longer winters at higher latitudes. In the Arctic, only a very able hunter could support a second wife. 

Higher latitudes meant not just fewer men on the mate market but also fewer men altogether. Because women could not supply as much food and because the land supported less wildlife, men had to hunt for a longer time over longer distances, with the result that more of them died from falls, drowning, starvation, and cold. Women thus faced a competitive mate market and strong sexual selection. This was especially so on the continental steppe-tundra of the sub-Arctic, where almost all food came from long-distance hunting. 

During the last ice age, this steppe-tundra covered more territory, stretching from the plains of Europe to Alaska. But it was continuously inhabited only at its western end. The climate was milder there because the Scandinavian icecap had pushed the steppe-tundra to the south and because the Atlantic Ocean provided warmth and moisture. These conditions favored a lush growth of grasses, mosses, lichens, and low shrubs, which supported large herds of herbivores and, in turn, a large human population. The climate was less favorable east of the Urals, in Asia, where the steppe-tundra was colder and drier because it was located farther north and farther from the Atlantic's moderating influence. As a result, the human population was smaller and more vulnerable to extinction, particularly during the glacial maximum.

In sum, the European steppe-tundra was a singularity among the many environments that confronted early humans as they spread around the world. Food was abundant but accessible only to males of hunting age, whose ranks were thinned by hunting deaths. A surplus of single women developed, partly because men were fewer in number and partly because men could not easily bear the cost of providing for a second wife and her children. Women thus had to compete against each other for a smaller number of potential mates, the result being strong sexual selection for those women with eye-catching characteristics.

Ancient DNA

Today, this is the same region where the skin is whitest and the hair and eyes most diversely colored. Here, too, the earliest evidence of this color scheme has been found in ancient DNA from human remains. Initially, it was thought that blue eyes arose among the hunter-gatherers of the Mesolithic and white skin among the farmers of the Neolithic. This view has been challenged by genetic evidence of white skin, red hair, blonde hair, and blue eyes in the remains of Mesolithic hunter-gatherers from Scandinavia and Russia. It seems that some people already had the European color scheme at that early date, but only in the north and east of Europe.

But when exactly did this color scheme develop? Probably earlier still—sometime between the earliest Mesolithic evidence (8,000 years ago) and Kostenki Man (circa 37,000 years ago), who still had dark skin, dark eyes, and an African facial shape. As we retrieve more ancient DNA, we may narrow this timeframe, perhaps to the last ice age (circa 10,000 to 25,000 years ago) when steppe-tundra covered the plains of northern and eastern Europe ... and where men were a critical resource in limited supply.

That is a big change over a short time. If sexual selection had not been the cause, what else could have been? The need to adapt to weaker sunlight and a colder climate? Why, then, did this evolution not happen among indigenous peoples who live just as far north in Asia and North America? In any case, why would a northern climate favor a proliferation of new hair and eye colors?

Future research

We cannot go back in time to see why early Europeans changed so fast and so radically. But we can question "witnesses" from that time. As we have seen, one witness is ancient DNA, and this research is ongoing.

Another witness is sex linkage. If sexual selection had acted on early European women, it should have directly modified their physical appearance. Since most genes have little or no sex linkage, this selection would have also indirectly modified the appearance of early European men. But there should still be some signs of sex linkage. We know, for example, that blue eyes are associated with a more feminine face shape. Other examples probably remain to be found.

Finally, there is the witness of culture. Single women, typically virgins, hold an unusual importance in the myths, folklore, and traditions of Europe. In this, we may see an echo of a time when many women never married and became oriented toward communal tasks, such as tending camp fires or acting as seers, sibyls, oracles, and the like. That period of prehistory may have influenced the subsequent course of cultural evolution, thereby giving women a greater role in society at large than they otherwise would have.

Reference

Frost, P. (2015).Загадка цвета кожи, волос и глаз у европейцев, Куьтура ВРН, July 7, translated by Dr. Yuri Lozotsev.

http://culturavrn.ru/world/15780