Denisovan admixture facilitated environmental adaptation in Papua New Guinean populations

Neandertals and Denisovans, having inhabited distinct regions in Eurasia and possibly Oceania for over 200,000 years, experienced ample time to adapt to diverse environmental challenges these regions presented. Among present-day human populations, Papua New Guineans (PNG) stand out as one of the few carrying substantial amounts of both Neandertal and Denisovan DNA, a result of past admixture events with these archaic human groups. This study investigates the distribution of introgressed Denisovan and Neandertal DNA within two distinct PNG populations, residing in the highlands of Mt Wilhelm and the lowlands of Daru Island. These locations exhibit unique environmental features, some of which may parallel the challenges that archaic humans once confronted and adapted to. Our results show that Denisovan-like haplotypes exhibit increased levels of population differentiation between PNG highlanders and lowlanders. The highly differentiated haplotypes, more common among highlanders, reside in genomic areas linked to brain development genes. Conversely, those more frequent in lowlanders overlap with genes enriched in immune response processes. Furthermore, Denisovan-like haplotypes displayed pronounced signatures of diversification within the major histocompatibility complex. Our findings suggest that Denisovan DNA has provided a valuable source of genetic variation to PNG genomes that facilitated adaptive responses to environmental challenges.