Although both natural and sexual selection have played a part in the evolution of the blue-eyed blonde, sexual selection was probably the primary force.Īs regards natural selection, depigmentation allows greater penetration of the skin by ultraviolet B (UVB), which is needed to synthesise previtamin D3. The traits are thought to have evolved among northern European tribes at the end of the last ice age. It has been theorised that the blonde hair and blue eyes seen in Caucasians are recent adaptations, dating from approximately 11,000 years ago. There is no single gene for blue eyes and blonde hair, but these adaptations are often found expressed together because the genes for each trait are located close together on the same chromosome. Individuals with lower levels of a melanin pigment called eumelanin are likely to have blonde hair. Research on variation in human hair colouration has shown that mutations in genes that are involved in the synthesis of melanin pigments are largely responsible. Today there are plenty of theories about the evolution of blonde hair and the science of genetics has furthered the debate. Unfortunately he was unable to find enough data to support his theory that blonde hair is sexually selected and had to drop the subject. Ten years after he published On the Origin of Species in 1859, Darwin started to research the sexual selection of blonde hair in women in preparation for his book The Descent of Man and Selection in Relation to Sex, which was published in 1871. Ask Carole: Chimpanzee wearing spectacles Photograph: Public Domain