Ancient South American genomes reveal a surprising connection to extinct human relatives: Neanderthals and Denisovans. This discovery, based on analysis of human remains from Brazil, Panama, and Uruguay, challenges existing understandings of ancient South American ancestry and migration patterns. It marks the first reported instance of Denisovan and Neanderthal ancestry in ancient South Americans. The research is published in the Proceedings of the Royal Society B.
Lead author Andre Luiz Campelo dos Santos, an archaeologist at Florida Atlantic University, explains that this genetic presence likely stems from interbreeding between anatomically modern humans, Neanderthals, and Denisovans, occurring thousands of years before humans migrated to the Americas via Beringia. The study not only supports existing archaeological evidence of north-to-south migration in South America but also suggests migrations occurred in the opposite direction, along the Atlantic coast.
Comparative Genomic Analysis Reveals Ancient Connections
The research team compared genomes from ancient human remains found in Brazil, Panama, and Uruguay with those from across the United States (including Alaska, representing ancient Beringia), Peru, and Chile. Two ancient whole genomes, sequenced from teeth discovered in northeast Brazil, were newly included in this study. The analysis also incorporated present-day worldwide genomes and DNA sequences from Denisovan and Neanderthal remains found in Russia.
The Pedra do Tubarāo site in northeast Brazil.Archaeological excavations at Pedra do Tubarāo, northeast Brazil, contributed to the study. Photo: Courtesy of Henry Lavalle and Desiree Nascimento, Universidade Federal de Pernambuco
The ancient remains analyzed ranged from just 1,000 years old to over tens of thousands of years old (Neanderthals disappeared from the fossil record approximately 40,000 years ago). The study revealed segments of Neanderthal and Denisovan DNA within the ancient South American genomes. Intriguingly, Australasian genetic signals were also detected in the remains of an individual from Panama. This same Australasian signal, previously identified in ancient remains from southeastern Brazil, is also present in the modern-day Sirui people of the Amazon.
Denisovan Ancestry and Australasian Signals: Unraveling the Mystery
Laurits Skov, a researcher at the Max Planck Institute for Evolutionary Anthropology (not affiliated with the study), notes that the higher levels of Denisovan ancestry observed in some populations align with additional ancestry from Papuans. He emphasizes the future importance of pinpointing when this Australasian ancestry component first appeared in the Americas and the extent of Denisovan/Neanderthal ancestry it carried.
The ancient individuals from Panama and Brazil displayed stronger Denisovan ancestral signals than Neanderthal-specific ancestry. This contrasts with the present-day human population, which generally exhibits more Neanderthal than Denisovan ancestry.
Study co-author John Lindo, an anthropologist at Emory University, explains that the Denisovan ancestry integrated into the South American human lineage as far back as 40,000 years ago, with its genetic signal persisting in the remains of a 1,500-year-old individual from Uruguay.
The absence of the Australasian signal in ancient North American remains suggests that ancient Australasians may have reached the Americas without traversing Beringia. This prompts further investigation into more ancient Native American and present-day Polynesian genomes.
Rewriting the Story of Human History
Iosif Lazaridis, a geneticist at Harvard University (not affiliated with the study), acknowledges the perplexing nature of the Australasian ancestry in the Americas, given its appearance in isolated samples across vast distances and time periods, lacking a clear pattern. He suggests a potential link to Austronesian migrations across the Pacific, a non-Beringian route, given their seafaring capabilities. However, there’s currently no evidence of Austronesians reaching the Americas.
The ongoing sequencing of ancient genomes continues to reshape our understanding of human history. These findings highlight the intricate interplay of genetic contributions from extinct hominin species, offering a more comprehensive picture of human dispersal across continents and challenging the notion of Homo sapiens as the sole contributor to our genetic makeup.
