American Indian origins complicated by ancient boy's DNA

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American Indians may have a more complex pool of ancestors than scientists once thought, according to a 24,000-year-old arm bone found in Siberia.

A DNA sample from the bone showed it belonged to a boy who was more closely related to American Indians and people living today in Europe and Western Asia than to East Asians, according to a paper published today in the journal Nature.

The finding may mean that American Indians have European genes that predate Christopher Columbus and subsequent western migrations to the Americas. Most experts have thought that American Indians came from east Asia, so another set of ancestors may need to be accounted for, said Joshua Akey, who specializes in evolutionary genomics at the University of Washington School of Medicine in Seattle.

"There's been enormous controversy in the origins and ancestry of Native American populations," Akey, who wasn't involved in the research, said in a telephone interview. "This study suggests a much more complicated and rich history than previously imagined."

About 14 percent to 38 percent of American Indian ancestry may have originated from the population to which the Siberian boy belonged, according to today's report. In fact, when the researchers mapped the bone's genes, they suggested that all 48 modern American Indian populations were equally related to the boy's sample.

The finding may also explain why skulls from early American Indian groups have characteristics that don't fit with East Asian ancestry, wrote the researchers, led by Eske Willerslev of the University of Copenhagen.

Sex chromosome

The boy's DNA, from what may be the oldest modern human genome to date, was closest to the hunter-gatherers of the Late Stone Age, from 50,000 to 10,000 years ago. The Y chromosome, the sex chromosome present in men, belongs to an ancestry that predates modern western Eurasians, the study found. There was no close relationship between the sample and modern east Asians.

A second DNA sample, from a 17,000-year-old arm bone also found in Siberia, showed similarities to the older DNA, though it was less reliable, as the genetic material had been contaminated by present-day DNA, the researchers said.

The site where the 24,000-year-old young male's bones were found is called Mal'ta, for a nearby village in south-central Siberia. The area may be the oldest in Siberia, and was excavated from 1928 to 1958, the authors wrote.

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