DNA reveals new wrinkle about settlement of Americas

Genomic analysis of ancient and modern peoples in the Americas suggests one founding migration wave, a study says. Another, published Tuesday in Nature, suggests that some early Native Americans may have had genetic roots in Australia and its neighboring islands, a region known collectively as Australasia.

Both groups of scientists agree, despite their differences, that Native Americans can trace their ancestry to Eurasian migrants having Australasian ancestry.

This exodus most likely began between 20,000 and 40,000 years ago.

David Meltzer, an archaeologist at Southern Methodist University in Dallas and a coauthor of the Science paper, said that researchers in his field had been wrestling with the early history of the Americas for centuries – debating when the first settlers arrived here, whether there were pulses of migrations, and so on.

Later migrations of Aleuts and Eskimos occurred approximately 9,000 and 4,000 years ago. From there, this main emigrant population would have split and diversified into many different first cultures.

Given that the earliest evidence for the presence of humans in the Americas dates to 15,000 years ago, the first ancestors may have remained in Beringia for about 8,000 years before their final push into the New World, the team said.

The exact process by which humanity introduced itself to the Americas has always been controversial. “But there has always been this question of how statistically informative this morphology is, and to what extent this actually reflects population relationships”.

The original Americans came from Siberia in a single wave no more than 23,000 years ago, at the height of the last Ice Age.

But diversification into the distinct tribes we know today, happened only after arrival in the Americas, not before. “But perhaps this is one step toward an explanation”.

“I think nearly no geneticists would have expected this”, Skoglund says. Now, DNA from modern-day people indicates that another population also crossed the land bridge and contributed to the heritage of some modern-day natives of Amazonian Brazil, researchers say.

Prior to the advent of cheap DNA sequencing, there were all sorts of ideas regarding the peopling of the Americas. But the “how” and “when” are confined to mystery.

This genetic data “is a clock that ticks”, said Nielsen.

The paper provides the first robust evidence that some native populations of the Americas trace part of their ancestry to a second source, said Deborah Bolnick of the University of Texas at Austin, who was not involved in the work.

“How America was populated in one of the most contentious topics in anthropology”. They just don’t see eye-to-eye on the interpretation of the information. His team analyzed partial genome sequences of 106 Native Americans from 25 populations in Central and South America, and compared them with DNA data from 197 populations from outside the Americas.

“We wanted to test it by dating the divergence time – that is, the split time between populations that now live in Siberia and East Asia, and the Native Americans“, Nielsen says. “They came from Siberia”. So clearly there was no 15,000-year Beringian standstill.

These became the groups which anthropologists refer to as Amerindians (American Indians) and Athabascans (a native Alaskan people). And the two groups disagree about how it got there. But as simple as the finding seems to be, Rasmus says it is truly astonishing. The study doesn’t account for Inuit populations in the north because they arrived later, bringing a distinctive culture with them.

“If we find that [genetic] signal, OK – there’s our answer”, he said.

According to the report published in Science, the conclusions of this new research change fundamentally what scientists previously thought. He searched the world for other copies of that fingerprint and found it far away – in modern Australasia. While there’s general agreement on the most important migration-across the Bering land bridge at the end of the last ice age-there’s a lot of arguing over the details. But do these individuals actually have any genetic affinity with Australians and Melanesians? Specifically, they looked at their mitochondrial DNA (mDNA), which is passed from mother to child.

But these studies have left open the possibility that other populations have made a small contribution to specific groups within the Americas.