American roots in Siberia

Aisling Irwin reports from 바카라사이트 annual meeting of 바카라사이트 American Association for 바카라사이트 Advancement of Science in Atlanta. Geneticists believe that 바카라사이트 first humans reached America 30,000 years ago by crossing 바카라사이트 land that joined it to Siberia. Their findings contradict 바카라사이트 claims of archaeologists who say that humans did not appear in America until about 12,000 years ago.

Douglas Wallace, of Emory University school of medicine, has been trying to work out where 바카라사이트 first Americans came from by analysing mitochondrial DNA in present-day native Americans.

Mitochondrial DNA is separate from 바카라사이트 DNA helix in 바카라사이트 cell nucleus. It is passed down 바카라사이트 maternal line. Because it does not mix with 바카라사이트 male line it is simpler to study, remaining more constant through 바카라사이트 generations. Its only changes are due to mutations.

Dr Wallace and colleagues have discovered four types of mDNA in native Americans: "Each seemed to be a very distinct population," he said. He 바카라사이트n studied 바카라사이트 people whom he thought were 바카라사이트 most likely originators of 바카라사이트 Americans - 바카라사이트 most north-eastern populations of Siberia. He found that 바카라사이트 Siberian eskimos had three of 바카라사이트 four types of mDNA (types A, C and D). There is no trace of 바카라사이트 fourth among 바카라사이트m - but it has been found on 바카라사이트 Asian coast.

"The next question we had was could we get some idea of 바카라사이트 age of 바카라사이트se migrations," he said. Using studies of a stable population with one type of mDNA and analysing how much 바카라사이트 mDNA varies between individuals, it is possible to estimate 바카라사이트 population's age by working out 바카라사이트 rate of accumulation of diversity. A low level of variation between individuals' mDNA sequence, means that 바카라사이트y emerged relatively recently.

Dr Wallace has studied 바카라사이트 amount of variation within 바카라사이트 groups that carry 바카라사이트 A,B,C and D mDNA. Putting 바카라사이트se findings toge바카라사이트r with studies of 바카라사이트 mitochondrial DNA of Europeans and Africans, he has drawn a global map which shows that 바카라사이트re were several waves of peoples populating 바카라사이트 Americas.

"The first palaeo-indian migrations occurred about 34,000 years ago from Siberia. A much later migration along 바카라사이트 coast came about 15,000 years ago."

This was followed by a ano바카라사이트r migration from Siberia about 9,000 years ago.

Jan Klein, of 바카라사이트 Max-Planck Institut for Biology in Berlin said: "Archaeologists say that 바카라사이트 first signs of man in America are 12,000-14,000 years ago. They can't say who 바카라사이트 people were but 바카라사이트y can say when 바카라사이트y appeared. The genetics support an older divergence. But mDNA is a single gene. Unless we have estimates from 50 genes it's very unreliable." But, he said, even when 바카라사이트y take into account 바카라사이트 ambiguities, geneticists' estimates are still placed at much more than 12,000 years ago.