Paabo and Reich’s studies clearly showed that early modern humans must have bred with other ancient groups as they left Africa and swept around the world. But while they proved that Neanderthal and Denisovan genes are still around, they said little about what these genes are doing. Are they random stowaways or did they bestow important adaptations?
When I spoke to Reich about this earlier this year, he was starting to sift through the data. “To a first approximation, they are random,” he said. “It’s possible that modern humans could have used the Neanderthal or Denisovan material to adapt to their environment, but we don’t have evidence for that.” However, palaeontologist Chris Stringer offered an intriguing suggestion: “If Denisovans were in South-East Asia long-term, they would have evolved immunities and defences to some of the diseases there, like different forms of malaria. That’s something modern humans could have picked up that would’ve been useful.”
He might have been right. Laurent Abi-Rached from Stanford University has just published a new study suggesting that our immune system owes a debt to our ancestors’ trysts with Neanderthals and Denisovans.