A new genetic study has found that the first Americans carried DNA from Denisovans, an ancient human species that resided in Asia more than 30,000 years ago. Researchers stated that this inherited genetic material may have helped early populations in the Americas adapt to unfamiliar diseases and environments.
The study, published in the journal Science, focused on a gene called MUC19, which plays a role in producing mucus and potentially influences how the body responds to pathogens.
Scientists discovered that approximately one in three people of Mexican ancestry today carries a version of this gene that closely resembles the Denisovan variant. This finding supports the theory that early humans arriving in the Americas brought Denisovan DNA with them, likely through earlier mixing with Neanderthals.
Fernando Villanea, a population geneticist at the University of Colorado Boulder and co-author of the study, explained that the Denisovan variant appears to have reached modern humans through Neanderthals.
The team described the gene’s structure as resembling a sandwich, with Denisovan DNA nestled between Neanderthal segments. This marks the first known case of a Denisovan gene entering the human genome via Neanderthals.
Tracing ancient DNA in modern populations
To explore whether this variant had a biological advantage, researchers analyzed genetic data from people of Mexican, Peruvian, Colombian, and Puerto Rican descent, as well as sequences from 23 ancient Indigenous individuals, three Neanderthals, and one Denisovan. The modern DNA came from the 1000 Genomes Project, while the ancient samples dated back to before the 13th century.
The Denisovan-linked MUC19 variant appeared in roughly 33% of Mexicans, 20% of Peruvians, and only about 1% of Colombians and Puerto Ricans. Researchers believe this pattern reflects varying levels of Indigenous American ancestry, which is highest on average in people of Mexican descent.
As scientists traced the genetic lineage, they found that the Denisovan segment within MUC19 has increased in length over generations. This suggests natural selection may have favored it, possibly due to its immune-related function.
Emilia Huerta-Sanchez, a population geneticist at Brown University and co-author of the study, said the variant may help regulate immune responses or defend against specific pathogens in ways that differ from the modern version.
Villanea and his team plan to investigate further using new biological datasets that combine genetic and physical trait information from Latino and Indigenous American individuals. They hope to understand how ancient DNA affects health and disease in modern populations.