The genome of a man who lived on the western coast of Greenland some 4,000 years ago has been decoded, thanks to the surprisingly good preservation of DNA in a swatch of his hair so thick it was originally thought to be from a bear.

This is the first time the whole genome of an ancient human has been analyzed, and it joins the list of just eight whole genomes of living people that have been decoded so far. It also sheds new light on the settlement of North America by showing there was a hitherto unsuspected migration of people across the continent, from Siberia to Greenland, some 5,500 years ago.

The Greenlander belonged to a Paleo-Eskimo culture called the Saqqaq by archaeologists. Using his genome as a basis, a team of researchers from the University of Copenhagen determined that the Saqqaq man’s closest living relatives were the Chukchis, people who live at the easternmost tip of Siberia. His ancestors split apart from Chukchis some 5,500 years ago, according to genetic calculations, implying that the Saqqaq people’s ancestors must have traveled across the northern edges of North America until they reached Greenland.

The team, led by Morten Rasmussen and Eske Willerslev of the University of Copenhagen, decoded the genome from four tufts of hair dug out of the permafrost at Qeqertasussuk, on the west coast of Greenland. The hair was excavated in 1986 and kept in a plastic bag in the National Museum of Denmark. It was found with other waste, and the scientists speculate that it was the result of a haircut.

There it moldered, unfrozen, until discovered by Dr. Willerslev, an expert on ancient DNA. Having spent two months digging for ancient human DNA in Greenland without finding any human remains, he concluded that ancient Greenlanders must have disposed of their dead by laying them on the sea ice. Only on complaining of his bad luck to a friend did he learn that the friend’s father had found the hair sample 20 years earlier.

No traces of the Saqqaq people have been found in North America, said Michael H. Crawford, an expert on circumpolar populations at the University of Kansas and a co-author of the report. Because the land bridge that once connected Siberia and Alaska had long since foundered, the Saqqaq people might have crossed to Alaska on the winter ice or could have used the boats on which they hunted fish and seals. They evidently kept to Arctic latitudes, perhaps because more southerly regions were already occupied by the Inuit, or because they were better adapted to life in the Arctic, Dr. Rasmussen said.

The Saqqaq man’s genome is so complete that the Danish researchers have been able to reconstruct his probable appearance and susceptibility to disease from the genetic information in his genome. They conclude that he would have had brown eyes because of variations, at four positions along his DNA, that are associated with brown eye color in East Asians.

He has the East Asian version of a gene known as EDAR, which endows people with hair that is thicker than that of most Europeans and Africans. Another gene suggests that he would have had dry earwax, as do Asians and Native Americans, not the wet earwax of other ethnic groups.

Perhaps reflecting the so far somewhat limited reach of personal genomics, the researchers note that the ancient Greenlander was at risk for baldness, a surprising assessment given that all that remains of him is his hair. Dr. Rasmussen said he assumed the man died young.

Biologists used to think that DNA would be found only in the cells at the roots of the hair, not in the keratin of which the hair shaft is made. But it now seems that the cells become incorporated into the growing shaft and their DNA is sealed in by the keratin, protecting it from attack by bacteria and fungi.

The Danish researchers, using an advanced DNA sequencing technology developed by Illumina of San Diego, reported that they were able to decode 80 percent of the ancient Greenlander’s genome to a high degree of accuracy. Their findings appear in the journal Nature.

An ever present danger in analyzing ancient human DNA is contamination, particularly from modern human DNA from all the archeologists and curators who have touched the samples. The Danish researchers said they took precautions to exclude this and other contaminants, and they seem to have succeeded.