In the late 1990s, scientists discovered that a gene mutation causes redheadedness. Specifically, it’s a variant of the melanocortin 1 receptor (MC1R), one of the key proteins that determines hair and skin color. The mutated gene is recessive, so in order for someone to have red hair, she has to inherit two copies of the gene, one from each parent.
Lots of people, especially those with Northern European ancestry, carry one copy of MC1R, but relatively few carry the two copies required for flaming tresses. Red hair can occur in any ethnicity, but the greatest concentration of redheads originates in Northern Europe. Scotland has the highest percentage of natural redheads, with 13 percent and Ireland is a close second, with 10 percent. Only about 2 percent of people in the United States have naturally red hair.