A Complicated Tale: The Ancient Indigenous People's Migration to South America

Not more than 25,000 years ago were North and South America populated. The fundamental idea of a north-to-south migration is turned on its head by new study and Neanderthal and Denisovan fossil data.

Dec 7, 2022

Aside from the poles, we are aware that the Americas were the last two continents that were peopled. We also know that neither North nor South America were inhabited for a very long time, just about 25,000 years, according to archeological evidence (maybe 37,000 years ago?). During the latter stage of the Pleistocene epoch, a time period known as the Last Glacial Maximum, modern people first congregated in central Asia, near Mongolia, and subsequently traveled to North America…. Because a large portion of the ocean was then blocked by glaciers, water levels were significantly lower at the period, resulting in a vast land bridge connecting Asia and Alaska.

According to prior research, there were numerous intricate migration routes that resulted the peopling of the Americas. Archaeologists already know that a north-to-south movement resulted in the population of South America, but new research1 reveals where ancient Indigenous people may have gone next. Recent, a new study reveals genetic commonalities between the ancient populations of Brazil, Panama, and Uruguay. These parallels show that Indigenous populations moved in the opposite way, from south to north, via the Atlantic coast, roughly a thousand years ago. This is the first instance where a migration from south to north is shown.

The authors compared two recently sequenced ancient human genomes from two distinct places in Brazil with global genomes from today and additional ancient entire genomes from North and South America. The genetic diversity in these novel genomes was quite rich. Neanderthal DNA was found by the authors, demonstrating that modern humans and Neanderthals most likely interbred in Asia before their offspring crossed the land bridge. Researchers also discovered evidence of the extinct Denisovan species of prehistoric humans, which lived in Asia in their samples. Actually, it was very surprising as they discovered a larger percentage of Denisovan DNA than Neanderthal DNA!

Figure 2. Deep ancestries of the ancient individuals of the Americas. (a) Quantile–quantile plots of the Z-scores for the D-statistic test for each ancient sample, a non-American, non-African population ‘X’ from Simons Genome Diversity Project (SGDP) [26] and the Mixe [26], compared to the expected ranked quantiles for the same number of normally distributed values. Each data point represents a distinct population from SGDP. Dashed red lines represent significance thresholds. (b) Archaic ancestry in ancient South America and Panama. Pie chart radius reflects the proportion of shared archaic loci in the individual. (Online version in colour.)

One ancient sample from Panama even included genetic evidence of Papua New Guinean and Australian Indigenous people. Although these genetic signatures had previously been discovered in prehistoric Amazonians, they have never been discovered in Central Americans. Stranger still, no samples from North America contain these markers.

This new research informs us that the story is considerably more complicated and adds intricacy to the fundamental idea of a north-to-south migration. A more thorough understanding of how exactly humans arrived in South America, including the routes they traveled to cross the continent and when these migrations took place, is the first step in getting beyond generalizations like "people moved down there."

However, in many ways, this study raises more questions than it does answers. How, for instance, did lineages from Australia and Papua New Guinea come up in South America with an ocean between them? And why, in some of the samples, is Denisovan DNA more prevalent than Neanderthal DNA?

The authors plan to provide answers to these queries in the future. The results do demonstrate that migration paths were complex and had various dimensions, despite the fact that there is still much we don't know. The authors claim that although this region of the world contains some of the most abundant and diverse DNA samples, we still know the least about the history of how humans came to be there.

Campelo Dos Santos, A. L., Owings, A., Sullasi, H. S. L., Gokcumen, O., DeGiorgio, M., & Lindo, J. (2022). Genomic evidence for ancient human migration routes along South America’s Atlantic coast. Proceedings. Biological Sciences, 289(1986), 20221078. https://doi.org/10.1098/rspb.2022.1078