Americans may be of East Asian descent

November 27th, 2007 - 3:54 pm ICT by admin  

Washington, November 27 (ANI): Anthropologists and archaeologists have always mooted whether a relatively small number of people from Siberia who trekked across a Bering Strait land bridge about 12,000 years ago gave rise to the natives of North and South America, or it was the result of an influx of people from other parts of Asia or Polynesia by land and sea, which began about 30,000 years ago.

Now, a genetic study led by University of Michigan scientists has produced new evidence that supports the land bridge theory.

Published online in PLoS Genetics, this study is one of the most comprehensive analyses so far among efforts to use genetic data to shed light on the topic.

The researchers examined genetic variation at 678 key locations or markers in the DNA of present-day members of 29 Native American populations across North, Central and South America. Data from two Siberian groups were also analysed during the study.

The study has shown that the genetic diversity, as well as genetic similarity to the Siberian groups, decreases the farther a native population is from the Bering Strait.

This finding supports the existing archaeological and genetic evidence that the ancestors of native North and South Americans came by the northwest route.

Another finding of the study is that a unique genetic variant is widespread in Native Americans across both American continents, which suggests that the first humans in the Americas came in a single migration or multiple waves from a single source, not in waves of migrations from different sources.

The variant, which is not part of a gene and has no biological function, has not been found in genetic studies of people elsewhere in the world except eastern Siberia.

According to the researchers, the variant might have occurred shortly prior to migration to the Americas, or immediately afterwards.

We have reasonably clear genetic evidence that the most likely candidate for the source of Native American populations is somewhere in east Asia, says Dr. Noah A. Rosenberg, assistant professor of human genetics and assistant research professor of bioinformatics at the Center for Computational Medicine and Biology at the U-M Medical School and assistant research professor at the U-M Life Sciences Institute.

If there were a large number of migrations, and most of the source groups didnt have the variant, then we would not see the widespread presence of the mutation in the Americas, he says.

In a previous study, Rosenberg had studied the same set of 678 genetic markers in 50 populations around the world to learn which populations were genetically similar, and what migration patterns might explain the similarities.

The current research, as far as North and South America are concerned, breaks new ground by looking at a large number of native populations using a large number of markers.

It also hints at supporting evidence for scholars who believe early inhabitants followed the coasts to spread south into South America, rather than moving in waves across the interior.

Assuming a migration route along the coast provides a slightly better fit with the pattern we see in genetic diversity, Rosenberg says. (ANI)

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