“Originally, we all had brown eyes”, said Prof Hans Eiberg from the University of Copenhagen, who led the team.
Blue eye colour most likely originated from the near east area or northwest part of the Black Sea region, where the great agriculture migration to the northern part of Europe took place in the Neolithic periods about six–10,000 years ago.
“That is my best guess,” he said. “It could be the northern part of Afghanistan.”
The mutation affected a gene called OCA2 and “literally 'turned off' the ability to produce brown eyes”, he says. OCA2 is involved in the production of melanin, the pigment that gives colour to hair, eyes and skin.
The mutation in the adjacent gene does not switch off the OCA gene entirely but limits its action, reducing the production of melanin in the iris of the eye – “diluting” brown eyes to blue. If the OCA2 gene had been completely turned off, those who inherited this mutation would be without melanin in their hair, eyes or skin colour - albino.
For the study, Prof Eiberg’s team examined DNA in blue-eyed individuals in countries as diverse as Jordan, India, Denmark and Turkey.
His findings are the latest in a decade of genetic research, which began in 1996, when Prof Eiberg first implicated the OCA2 gene as being one of those responsible for eye colour.
“They have all inherited the same switch at exactly the same spot in their DNA. From this we can conclude that all blue-eyed individuals are linked to the same ancestor,” said Prof Eiberg, who reports the work in the journal Human Genetics.