Ancient DNA Hidden in Pacific Islanders Reveals Three Separate Encounters With a Mystery Ancestor
People living in Near Oceania, a region spanning New Guinea, surrounding island chains, and the main Solomon Islands, carry more ancient, pre-modern human DNA than any other population on Earth. New research has found that their ancestors inherited genetic material from three distinct Denisovan-like groups, extinct relatives of modern humans, across tens of thousands of years of prehistory. Some of that ancient inheritance appears to influence gene activity today, particularly in immune-related pathways.
While much of the world’s human population was spreading and connecting, the early settlers of Near Oceania arrived roughly 42,000 years ago and largely stayed put, cut off at the far edge of the inhabited world for tens of thousands of years. That long separation left deep marks in their DNA, including stretches of genetic code inherited from archaic human relatives that scientists are only now beginning to map. These populations have been dramatically underrepresented in major genetics studies, meaning these discoveries were hiding in plain sight for decades.
An international team, publishing in the journal Science, sequenced the complete genomes of 177 individuals from 12 diverse Near Oceanic populations and compared them with 1,284 genomes from populations around the world.
Sepik Islanders Carry 25 Times More Denisovan DNA Than East Asians
Oceanic genomes carried roughly two and a half times more ancient inherited sequence overall than European genomes. For Denisovan DNA specifically, Near Oceanic individuals carried 14 times more than East Asian people. One group, the Sepik of New Guinea, carried 25 times more Denisovan DNA than East Asians.
In total, the researchers reconstructed ancient inherited sequence covering more than 70% of what they could analyze of the archaic human genome, nearly 1.9 billion units of genetic code. Of that, 831.9 million units came from Denisovan lineages, almost three times more than prior research had identified. More than 505 million units of archaic sequence had never been documented before this study.
By examining fine-grained patterns of Denisovan DNA across modern genomes, the team identified signatures pointing to three distinct Denisovan-like groups that contributed DNA to the ancestors of Near Oceanians at different points. The authors note that more work is needed to clarify exactly when and how each of those events unfolded.
Long Isolation Pushed These Populations Down a Genetically Distinct Path
Spending tens of thousands of years at the far edge of the inhabited world does something to a population’s DNA. Random genetic drift, the process by which chance alone reshapes the genetic makeup of a small, isolated group over many generations, has left some Near Oceanic communities dramatically different from everyone else on Earth.
Several populations, including the Baining groups of New Britain and communities in the Solomon Islands, show signs of severe population bottlenecks, meaning their numbers fell sharply at some point in history. Population modeling pointed to a strong bottleneck between 10,000 and 20,000 years ago in some groups, and a separate signal of slowed growth around 30,000 years ago in others.
Ancient Genes From a Vanished Ancestor Still Appear to Influence Immunity
Some of the ancient inherited DNA is not simply a historical relic. Several variants appear to have been actively favored by natural selection. Researchers scanned for those signals and found numerous candidates concentrated in immune-related genes.
Among the most notable was TRPS1, a gene involved in bone development, skull and facial structure, and hair. A version inherited from Denisovans appears at high frequencies, approaching 75% in some groups, across Oceanic and nearby island populations. Previous work identified selection on TRPS1 in central African rainforest hunter-gatherers and highland Ecuadorians, suggesting that different human populations may have experienced selection on the same gene under similar environmental pressures near the Equator.
Source : https://studyfinds.com/pacific-islanders-most-ancient-human-dna/