Science reports:

When modern humans first migrated from Africa to the tropical islands of the southwest Pacific, they encountered unfamiliar people and new pathogens. But their immune systems may have picked up some survival tricks when they mated with the locals—the mysterious Denisovans who gave them immune gene variants that might have protected the newcomers’ offspring from local diseases. Some of these variants still persist in the genomes of people living in Papua New Guinea today, according to a new study.

Researchers have known for a decade that living people in Papua New Guinea and other parts of Melanesia, a subregion of the southwest Pacific Ocean, inherited up to 5% of their DNA from Denisovans, ancient humans closely related to Neanderthals who arrived in Asia about 200,000 years ago. Scientists assume those variants benefited people in the past—perhaps by helping the modern humans better ward off local diseases—but they have wondered how that DNA might still be altering how people look, act, and feel today. It’s been difficult to detect the function of Neanderthal and Denisovan DNA in Melanesians, however, because scientists have analyzed so little genetic data from living humans in Papua New Guinea and other parts of Melanesia.

The new study overcomes that problem by using genetic data from 56 individuals from Papua New Guinea that were recently analyzed for another paper, part of the Indonesian Genome Diversity Project. The researchers, mostly from Australia and New Guinea, compared those genomes with those of Denisovans from Denisova Cave in Siberia, as well as Neanderthals. They found the Papuans had inherited unusually high frequencies of 82,000 genetic variants known as single nucleotide polymorphisms, which arise from differences of a single base or letter in the genetic code—from Denisovans. [Continue reading…]