Approximately 1% to 2% of the human population has red hair. Red hair is more frequent (between 2% and 6% of the population) in northern and western Europeans, and their descendants, and at lower frequencies throughout other parts of the world. These areas are high prevalence areas for MS.
Red hair appears in people with two copies of a recessive gene on chromosome 16 which causes a mutation in the protein called MC1R. Red hair is also associated with fair skin color, lighter eye colors, freckles, and sensitivity to ultraviolet light.
Bodmer and Cavalli-Sforza (1976) hypothesized that lighter skin pigmentation prevents rickets in colder latitudes by encouraging higher levels of Vitamin D production and also allows the individual to retain heat better than someone with darker skin. However, in 2000, Harding and colleagues, concluded that red hair was not the result of positive selection and instead proposed that it occurs because of a lack of negative selection.