How extinct humans left their mark on us
Most people in the world share 2-4% of DNA with Neanderthals while a few inherited genes from Denisovans, a study confirms.
Denisovan DNA lives on only in Pacific island dwellers, while Neanderthal genes are more widespread, researchers report in the journal Science.
Meanwhile, some parts of our genetic code show little trace of our extinct cousins.
They include hundreds of genes involved in brain development and language.
"These are big, truly interesting regions," said co-researcher Dr Joshua Akey, an expert on human evolutionary genetics from the University of Washington Medicine, US.
"It will be a long, hard slog to fully understand the genetic differences between humans, Denisovans and Neanderthals in these regions and the traits they influence."
Studies of nuclear DNA (the instructions to build a human) are particularly useful in the case of Denisovans, which are largely missing from the fossil record.
The prehistoric species was discovered less than a decade ago through genetic analysis of a finger bone unearthed in a cave in northern Siberia.
Substantial amounts of Denisovan DNA have been detected in the genomes of only a handful of modern-day human populations so far.
"The genes that we found of Denisovans are only in this one part of the world [Oceania] that's very far away from that Siberian cave," Dr Akey told BBC News.
Where the ancestors of modern humans might have had physical contact with Denisovans is a matter of debate, he added.
Denisovans may have encountered early humans somewhere in South East Asia and, eventually, some of their descendants arrived on the islands north of Australia.
Meanwhile, humans repeatedly ran into Neanderthals as they spread across Eurasia.
"We still carry a little bit of their DNA today," said Dr Akey. "Even though these groups are extinct their DNA lives on in modern humans."
The research was carried out by several scientists, including Svante Paabo of the Department of Evolutionary Genetics at the Max-Planck-Institute for Evolutionary Anthropology.
They found that all non-African populations inherited about 1.5-4% of their genomes from Neanderthals.
However, Melanesians were the only population that also had significant Denisovan genetic ancestry, representing between 1.9% and 3.4% of their genome.
"I think that people (and Neanderthals and Denisovans) liked to wander," said Benjamin Vernot of the University of Washington, who led the project.
"And yes, studies like this can help us track where they wandered."
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