We may have bred with Denisovans much more recently than we thought

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Humans 1 April 2019 , updated 2 April 2019

People in Papua New Guinea have some Denisovan DNA

USO/Getty

By Clare Wilson

Nossa espécie pode estar cruzando com os Denisovanos há 15 mil anos, de acordo com uma análise detalhada do DNA de pessoas que vivem na Indonésia e Papua Nova Guiné.

Nós já sabemos que, depois que o Homo sapiens migrou pela primeira vez para fora da África, nossa espécie cruzou várias espécies de hominídeos extintos, incluindo os neandertais e os denisovanos. Os sinais estão em nosso DNA hoje - todas as pessoas de ascendência não-africana carregam algum DNA de Neandertal, enquanto alguns povos asiáticos também possuem DNA de Denisovanos.

Not much is known about the mysterious Denisovans. Their only physical remnants discovered so far are a few teeth and fragments of bone unearthed in a cave in Siberia. But DNA analyses have found that the Denisovans must have lived much further east and south of Siberia too. Genetic evidence suggested our species interbred with Denisovans at least twice, in Asia and Australasia, and that the genomes of people from Papua New Guinea may be up to 5 per cent Denisovan. 

Until now, such genetic studies have generally looked at only a small fraction of people’s DNA to draw these conclusions. To get a fuller picture, Murray Cox of Massey University, New Zealand, and his colleagues have done the first large-scale study of whole genomes from people living in Indonesia and Papua New Guinea, sequencing all the DNA of 161 different people.

Read more: Siberian cave reveals secrets of its mysterious Denisovan inhabitants

This reveals that our ancestors in this part of the world seem to have interbred with at least two distinct groups of Denisovans – one group about 50,000 years ago, as previously thought, and a second group much more recently.

The genetic analysis suggests this occurred sometime between 50,000 to 15,000 years ago. There’s reason to think it happened at the most recent end of that range, says Cox. The genes from the second interbreeding are much more common in people living in the Papua New Guinea mainland than in people living on nearby islands, suggesting the mixing happened with the mainlanders after the islanders’ ancestors had left.

Evidências arqueológicas sugerem que essa migração para as ilhas aconteceu 30.000 anos atrás. Mas, comparando os genomas dos habitantes do continente e dos ilhéus, a equipe de Cox calcula que foi mais tarde, cerca de 15.000 anos atrás. A única explicação para os dados é que houve um surto de intercambistas continentais com Denisovans, diz Cox, que apresentou os dados na Associação Americana de Antropologia Física em Cleveland na semana passada..

Read more: Prehistoric girl had parents belonging to different human species

Cox doesn’t think any last remaining Denisovans could still be hiding out on an island. “It’s isolated, but it still has too much contact for something like that not to be noticed.”

The new data also reveals ­considerable genetic diversity among the Denisovans – the group involved in the earlier Papua New Guinea interbreeding are almost as genetically different to a Denisovan bone found in Siberia as they are to the Neanderthals, a completely different branch of the hominin family tree.

“This study is giving us insight into the real pattern of human diversity,” says John Hawks of the University of Wisconsin-Madison. “It opens a window to the fact that there was once a population that was as rich and diverse as modern humans that’s now gone.”

At the same conference, Bence Viola of the University of Toronto and colleagues revealed a newly identified piece of Denisovan bone, the first skull fragment to be discovered. “It indicates it was a pretty large individual,” says Viola.

The fragment is small, and raises more questions than it answers, says Viola. “But look at how our knowledge has exploded over the past nine years from a tiny fragment of finger bone.”