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.
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.
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.
The Catholic Church ban on cousin marriage also prevented inbreeding, which does a number on looks.