DNA analysis of human hair preserved in Greenland's permafrost has given clues as to what the owner looked like.

A study, published in the journal Nature, says the individual's genome is the oldest to have been sequenced from a modern human.

The researchers say the man, who lived 4,000 years ago, had brown eyes and thick dark hair, although he would have been prone to baldness.

They say the genome also shows that his ancestors migrated from Siberia.

The man has been named Inuk, which means "human" in the Greenlandic language.

"We wanted to acknowledge that he was from Greenland, even though he is not a direct ancestor of modern Greenlanders," said Professor Eske Willerslev from the University of Copenhagen, who took part in the study.

The researchers say an analysis of the genome shows that Inuk was from the Saqqaq culture.

The team now has genetic evidence that Inuk's metabolism and body mass meant he was adapted to living in a cold climate.

The Saqqaq hunted seals and seabirds and relied on the sea for most of their food. Archaeological remains show they lived in tiny tents in winter.

"It's a very hostile environment and I was really surprised that people could live up there," explained Professor Willerslev.

Inuk had shovel-shaped front teeth, according to the research team. He also had dry earwax, which would have made him more vulnerable to ear infections.

He is thought to have died young because, although his genes show susceptibility to baldness, tufts of thick hair were found.

Siberian connection

The analysis took a year and the genome sequence suggested that the Saqqaq's closest living relatives were native populations in north-eastern Siberia, such as the Chuckchis and the Koryaks. The scientists say the Saqqaqs were probably not ancestors of contemporary Inuit or Native American populations.

This suggests, the researchers say, that the Saqqaqs migrated from Siberia to the New World approximately 5,500 years ago. This would have been independent of the movement that gave rise to modern Native Americans and Inuit.

Professor Willerslev explained that it was not known how the people made the crossing from Siberia to Greenland and Alaska.

"There was no land bridge between Siberia and Alaska at that time, so they must have crossed either by boat or in the winter time over the ice. No one knows," he said.

What happened to the Saqqaq people and why they died out also remains a mystery. "Was it climatic change, was it competition from other cultures coming in? We have no idea," said Professor Willerslev.