There is a vivid debate if Native Americans from both South America and North America entered the continent in a single wave 12,000 years ago coming from Siberia through the Bering Strait land bridge or whether ancient Americans also came from other Asian areas or Polynesia, coming by sea as well as by land, starting 30,000 years ago. Paleontologists have found Negroid remains in South America older than 12,000 years, resembling Black races from southeastern Asia and Australia.
A team from the University of Michigan, based on a research published online in PLoS Genetics supports the land bridge theory. The scientists analyzed DNA variation at 678 markers in 29 modern Native American populations from North, Central and South America and two Siberian groups.
It appeared that genetic diversity, but also
genetic similarity to the Siberian groups, increases in populations closer to the Bering Strait, thus Amerindians arrived through the northwest route. An unique DNA stretch common in Amerindians across both Americas point that the first Amerindians in the Americas arrived in a single waves or multiple waves originating in a single source, not in waves of migrations from different sources. That DNA pattern, not functional, has been found only in eastern Siberian populations, outside Americas. The mutation could have happened shortly before those people entering Americas, or immediately afterwards (it must be considered that some tribes in Kamchatka peninsula are considered a back-migration of Amerindians).
"We have reasonably clear genetic evidence that the most likely candidate for the source of Native American populations is somewhere in east Asia," said 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 didn't have the variant, then we would not see the widespread presence of the mutation in the Americas," he said.
The same 678 genetic markers had been checked in 50 populations worldwide, to see genetic similarities between populations and which migration patterns could explain the similarities. "The pattern the research uncovered - that as the founding populations moved south from the Bering Strait, genetic diversity declined - is what one would expect when migration is relatively recent. There has not been time yet for mutations that typically occur over longer periods to diversify the gene pool. ", said co-first author Dr. Mattias Jakobsson, a post-doctoral fellow in human genetics at the U-M Medical School and the U-M Center for Computational Medicine and Biology.
The study also comes with proof that early Amerindians followed the shores to spread south into South America, not the continent's interior. Andean populations are closer to those of Central America; these populations are also more diverse than those of eastern South America. "Assuming a migration route along the coast provides a slightly better fit with the pattern we see in genetic diversity," said Rosenberg.
Still, the new research does not eliminate the theory of the ancient Negroid migration, nor a very recent wave from Polynesia (at least trade relationships), which could explain the presence of some animals, crops and common cultural elements with Malayo-Polynesian populations from southeastern Asia. It just explains how the typical Siberian-rooted American Indians migrated across the Americas.
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