It was merely a few decades ago that most ancient history books taught the theory that the first humans to occupy North American crossed a land bridge from Siberia to what is now Alaska, then migrated southward along the Pacific coast, continuing to Central America and South America. That simple explanation was supported by findings of evidence of what became known as the Clovis culture and that group became the accepted ‘first humans’ of the Americas. That theory began to be doubted as pre-Clovis evidence was found in North America, while signs of a completely different group of people began to appear in South America – people who traveled there via boats across the Pacific. That theory turned in a surprising new direction recently as researchers using DNA from two ancient human individuals unearthed in two different archaeological sites in northeast Brazil found the presence of DNA from Neanderthals and Denisovans. Even more surprising, they also uncovered the first evidence of a south-to-north migration up the Atlantic coast of South America. Does this change everything?
“An increasing body of archaeological and genomic evidence has hinted at a complex settlement process of the Americas by humans. This is especially true for South America, where unexpected ancestral signals have raised perplexing scenarios for the early migrations into different regions of the continent.”
A new study published in the journal Proceedings of the Royal Society B: Biological Sciences admits that the simple straight-line migration by the Clovis people from Siberia to Alaska down the Pacific coast all the way to Chile and Argentina was just too easy. Researchers from Florida Atlantic University and Emory University joined forces to find a better explanation. They began with genomes from ancient human remains in Alaska and the western United States which were most likely from the group that came from Siberia around 13,000 years ago. They compared these with ancient human genomes found in Brazil, Panama, and Uruguay. Finally, they were fortunate enough to get two new ancient whole genomes from 1000-year-old teeth found at two different locations in northeast Brazil – adding some Atlantic coast DNA to the mix. Following the straight migration theory, these should have all been very close or matching.
“We find a distinct relationship between ancient genomes from Northeast Brazil, Lagoa Santa, Uruguay and Panama, representing evidence for ancient migration routes along South America's Atlantic coast.”
Well, the South American DNA from the Pacific coast matched the DNA from its Atlantic coast. This is the first time such a connection has been made. The next question to be solved is how did these people get from coast to coast? For that, the researchers brought in Michael DeGiorgio, Ph.D., a co-corresponding author who specializes in human, evolutionary, and computational genomics and is an associate professor in the Department of Electrical Engineering and Computer Science within FAU’s College of Engineering and Computer Science. DeGiorgio and his team helped design a model to simulate how this migration would have occurred.
“Results of the study, published in the journal Proceedings of the Royal Society B. (Biological Sciences), suggest that human movements closer to the Atlantic coast eventually linked ancient Uruguay and Panama in a south-to-north migration route – 5,277 kilometers (3,270 miles) apart. This novel migration pattern is estimated to have occurred approximately 1,000 years ago based on the ages of the ancient individuals.”
This is truly a significant discovery – until now there has been no archeological or cultural evidence of a link between the people of the far northwest and the northeast or southeast coasts of Brazil, let alone Uruguay and Panama. There are plenty of opportunities for differences to develop -- individuals from southeast Brazil are about 9,000 years older than those from northeast Brazil, Uruguay and Panama; and the individuals from northeast Brazil, Uruguay and Panama were found thousands of kilometers apart. Yet … they are from the same genome. And that genome yields the next big shocker:
“Among the key findings, researchers also have discovered evidence of Neanderthal ancestry within the genomes of ancient individuals from South America. To further add to the existing complexity, researchers also detected greater Denisovan than Neanderthal ancestry in ancient Uruguay and Panama individuals.”
That’s right … the press release states that both Neanderthal and Denisovan genes were identified in these individuals, from the oldest to the 1000-year-old teeth in northeastern Brazil. Based on estimates of the extinctions of the Neanderthals and Denisovans, that mixing with modern humans occurred about 40,000 years ago. John Lindo, Ph.D., a co-corresponding author of the article who specializes in ancient DNA analysis and is an assistant professor in the Department of Anthropology at Emory University, puts it in perspective.
“It’s phenomenal that Denisovan ancestry made it all the way to South America. The admixture must have occurred a long time before, perhaps 40,000 years ago. The fact that the Denisovan lineage persisted and its genetic signal made it into an ancient individual from Uruguay that is only 1,500 years old suggests that it was a large admixture event between a population of humans and Denisovans.”
But wait … there’s more!
In an interview with Gizmodo, Laurits Skov, a researcher at the Max Planck Institute for Evolutionary Anthropology who was not affiliated with the study, points out that the DNA from one individual from Panama showed more Denisovan DNA than Neanderthal – the reverse of the proportion found just about everywhere else. This could indicate that the individual descended from Papuans, who also have high levels of Denisovan DNA. This discovery leaves the original source of the first humans in the Americas in a state of flux – while the Neanderthal DNA indicates migration from Siberia. The Denisovan supports the idea that Pacific islanders traveled in boats to the west coast of South America and settled there.
The biggest revelation of this new study is the evidence of the continuation of the north-south migration around the southern tip of South America, becoming a south-north migration that went up the east coast all the way to where one group of the first humans crossed – Panama. It took researchers from the disciplines of archaeology, biological sciences, genomics and computer science to solve this piece of the puzzle. We still have a long way to go in putting the entire picture of the populating of the Americas together.