A Stone Age man who lived about 7000 years ago and whose buried bones were discovered in 2006 has turned out to be the earliest known person with blue eyes, a physical trait that evolved relatively recently in human history, a study has found.
A DNA analysis of the man's tooth has also revealed that although he was more closely related to modern-day Scandinavians than to any other European group, he had the dark-skinned genes of an African, though scientists do not know his precise skin tone.
The man, who was about 1.7m tall and aged 30-35, was a Mesolithic hunter-gatherer rather than a farmer. He did not have the lactose-tolerance genes that allowed him to digest milk as an adult - a key sign that he had little or no contact with domesticated livestock.
His well preserved skeleton was one of two discovered in 2006 in a deep cave system called La Braa-Arintero near Len in northwest Spain, which is 1500m above sea level and cold enough to limit the bacterial decay of DNA.
Dating has placed the skeletons in the middle of the Mesolithic period, which lasted between 5000 and 10,000 years ago and represents the interlude between the older Palaeolithic and the more recent Neolithic, when agriculture and livestock farming spread from the Middle East and became widespread across Europe.
The study, published in the journal Nature, sequenced fragments of DNA extracted from the man's tooth, revealing that he carried an unusual combination of genes for blue eyes and dark skin as well as for slightly curly, dark-brown hair and lactose intolerance.
Dr Carles Lalueza-Fox of the Institute of Evolutionary Biology in Barcelona said: "Blue eyes in modern humans are related to the same mutation in a gene called HERC2. If you have this mutation in both copies of the chromosome, you will have blue eyes for sure."
It is not clear why blue eyes spread among ancient Europeans. One theory is that the gene could have helped to prevent eye disorders due to low light levels in European winters, or that the trait spread because it was deemed sexually attractive.