Ancient humans migrating

The migration of ancient indigenous peoples to South America is a complex story

We know that (excluding the poles) the Americas were the last two continents humans called home. We also know that archaeologically neither North America nor South America was inhabited so long ago – specifically, only about 25,000 years ago.

Modern humans congregated in Central Asia, around Mongolia, then traveled to North America during a period called the Last Glacial Maximum, in the last phase of the Pleistocene epoch. Back then, water levels were much lower because much of the ocean was trapped in glaciers, creating a massive land bridge between Asia and Alaska.

Read more: When did humans reach North America? The question is getting more and more complex

Research indicates complex sets of migratory routes that led to settlements throughout the Americas. Archaeologists already understand how the settlement of South America was the result of a north-south migration; but new research shows where ancient Indigenous peoples might have gone after that.

Intertwined routes

Researchers publishing in the Proceedings of the Royal Society Biological Sciences recently discovered genetic similarities among ancient peoples living in present-day Brazil, Panama and Uruguay. These similarities suggest that around a thousand years ago, the indigenous populations also migrated in the opposite direction: a migration from south to north, via the Atlantic coast.

“This is the first time we’ve proposed this south-to-north migration,” says study co-author Andre Luiz Campelo dos Santos, a postdoctoral researcher at Florida Atlantic University.

He and his colleagues compared newly sequenced genomes of two ancient humans, from two different sites in Brazil, with current global genomes and other ancient whole genomes from North and South America. These new genomes showed a wealth of genetic diversity, says Santos: “We found Neanderthal DNA, which shows that modern humans likely mated with Neanderthals in Asia and their descendants crossed the land bridge.

The researchers also found evidence of Denisovans, an extinct species of ancient hominids that lived in Asia. “We found a higher percentage of Denisovan DNA than Neanderthal DNA, which was totally unexpected,” Santos says. “[Though] we’re not quite sure what that means.

An ancient sample from Panama even harbored genetic traces of Indigenous Australians and Papua New Guinea. While these genetic signals have been found before in ancient Amazonians, this is the first time they’ve been found in Central America. Even stranger, these markers are not found in North American samples.

“The question becomes,” says Santos, “how [did] these signals are found in South and Central America without leaving traces in North America?’ »

A complex story

This new research adds complexity to the basic notion of a north-south migration and shows us that storytelling is much more involved, says Jennifer Raff, associate professor of anthropology at the University of Kansas who has not participated in the research.

“This is a solid and exciting addition to our knowledge of the first peoples of the Americas,” she says. “I’m really excited to see some of the finer detail of population movement added to our broad stroke models.”

Raff adds that this is also the first step in moving beyond claims like “and then people got to South America” ​​to a more accurate understanding of exactly how humans got there. below – including the routes they took to move across the continent and when these movements took place.

Yet, in many ways, this research raises even more questions than it answers. For example, with an ocean between them, how did the Australian and Papua New Guinean lineage end up in South America? And why is Denisovan DNA more important than Neanderthal DNA in some samples? These are questions that Santos and his team hope to answer in the future.

Although there is still a lot we don’t know, the results show that the migration routes were complex and had multiple dimensions. This region of the globe has some of the richest and most diverse DNA samples; yet it is also a part of the world where, according to Santos, we still know the least about the history of human origin.

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