Whether the redhead is auburn or strawberry depends on whether the mutation is based on black or fair hair. It is found among Celtic peoples, who are not always associated with northern, sunless climes. But it is also a characteristic of the Jewish tribe of Judah to which Jesus belonged. These people are Middle Eastern, an area with plenty of sun. The environmental theory breaks down here and even if all redheads were killed off, the gene would remain in the population – carried by some non- redheads. So that colour type would not become extinct.
Margaret E Salmond