At its root, the desire to have light hair represents an urge to look different, says Peter Frost, an anthropologist at Laval University in Quebec City. Most people have dark hair, so blondes stand out. The urge to be blonde may also be driven by deep evolutionary history beginning many millennia ago when light shades first appeared on women’s manes, allowing them to turn the heads of potential mates. ”The more common a hair color becomes, the less often it is preferred,” Frost said. “It’s a kind of novelty effect. The moment you become ordinary, you no longer have the same appeal. There’s selection for being a bit different and eye-catching.” Modern humans evolved in Africa. Even after migrating to Europe about 35,000 years ago, scientists think that all people had black hair. Then, sometime between 10,000 and 15,000 years ago in northern and eastern Europe, studies suggest, the hair-color gene MC1R developed variations that produced a diversity of hues, including red, brown and blonde.
Eye color, which is controlled by several genes, including one called OCA2, diversified at the same time. Some researchers have speculated that lighter hair and eyes helped people better acquire vitamin D in a high-latitude environment. Frost has a different theory.
During the last Ice Age, he proposes, men had to travel longer distances through Arctic tundra to find animals to hunt. That led to higher death rates for men as well as a decreased chance for polygamy because it would have been nearly impossible to support more than one family with such a scarcity of food.
As women came to outnumber the supply of monogamous men, they had to become more competitive for male attention. In evolutionary terms, this produced strong sexual selection for novel hair and eye colors. Women with unusually bright looks were eye-catching and appealing. Via Why Do So Many Women Go Blonde?