In Africa, for example, red hair is selected against because high levels of sun harm untanned skin.
However, in Northern Europe this does not happen, so redheads can become more common through genetic drift.
In species other than primates, red hair has different genetic origins and mechanisms.
Red hair is the rarest natural hair color in humans.
The pigment pheomelanin gives red hair its distinctive color.
Red hair has far more of the pigment pheomelanin than it has of the dark pigment eumelanin.
Abd ar-Rahman I also had red hair, his mother being a Christian Berber slave.
It occurs more frequently (2–6%) in people of northern or western European ancestry, and less frequently in other populations.
If one of these changes is present on both chromosomes then the respective individual is likely to have red hair.
This type of inheritance is described as an autosomal recessive mode of inheritance.
Red hair appears most commonly in people with two copies of a recessive allele on chromosome 16 which produces an altered version of the MC1R protein.
Red hair varies in hues from a deep burgundy or bright copper (reddish-brown or auburn) through to burnt orange or red-orange and strawberry blond.
In the United States, it is estimated that 2–6% of the population has red hair. In Asia, red hair has been found among the ancient Tocharians, who occupied the Tarim Basin in what is now the northwesternmost province of China.