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PNG in forefront of ancient Denisovan research

Neanderthals  Denisovans and our ancestors were mixing a long time ago
Denisovans (pictured) and our human ancestors were mixing 50,000 to 15,000 years ago - and some of our genetics can be traced back to these ancient humans.

CLARE WILSON | New Scientist

LONDON - Our species may have been interbreeding with Denisovans as recently as 15,000 years ago, according to a detailed analysis of the DNA of people living in Indonesia and Papua New Guinea.

We already know that, after Homo sapiens first migrated out of Africa, our species repeatedly interbred with a number of now-extinct hominin species, including the Neanderthals and Denisovans.

The signs are in our DNA today – all people of non-African descent carry some Neanderthal DNA, while some Asian people also have Denisovan DNA.

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% 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.

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.

Archaeological evidence suggests this migration to the islands happened 30,000 years ago. But, by comparing the genomes of mainlanders and islanders, Cox’s team calculates that it was later, at around 15,000 years ago.

The only explanation for the data is that there was an extra bout of mainlanders interbreeding with Denisovans, says Cox, who presented the data at the American Association of Physical Anthropology Conference in Cleveland last week.

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 PNG 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.”

Comments

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Philip Fitzpatrick

I don't know whether the gene shows up in Australian Aboriginal populations but if it doesn't then that lends credence to the 15,000 year theory given that the Aborigines arrived in Australia 50-65,000 years ago via either or both Timor and New Guinea.

Chris Overland

I think that it should be apparent by now that the whole notion of "pure bred" races of humans is an enormous intellectual fraud.

There has been so much inter breeding between the various different species of hominid that the idea of a pure line of descent is fanciful in the extreme.

The truth is that we are all related in some way: it is just a question of following our lineage back far enough

This is, of course, not a realistic prospect in reality but it takes no great intellectual effort to imagine how all our different lines of descent must lead back to a tiny handful of small and very, very nervous proto-primates.

How much less complicated human affairs could become if only we could get over our various notions of exceptionalism.

Sadly, we cling tenaciously to our self serving myths and legends that supposedly "prove" how special we are. We will demonise and victimise others based upon such beliefs and even fight and die for them.

I think that a visiting intergalactic anthropologist would regard us as a very strange species of creature, being both exceptionally bright and amazingly stupid at the same time.

Hopefully, research such as that described in this article will help erode the pernicious folly of imagined racial superiority that afflicts so much of the world.

Garry Roche

With regard to Denisovans and Neanderthals, judging from the occipital lump on the back of my skull, (and perhaps my red hair) I myself am home to some Neanderthal genes.

There was a time when calling a person a ‘Neanderthal’ would be considered an insult. Nowadays however more people are aware that many Europeans and Asians have some ‘Neanderthal’ genes in their system, in contrast to Africans who generally have no Denisovan or Neanderthal genes.

In brief, Europeans and Asians did interbreed with Neanderthals and Africans did not.

Ironically if it were the opposite case and it was Africans who had interbred, then some white supremacists have probably claimed to be of ‘purer superior stock’!

Apparently, Tibetans, like many Melanesians, have traces of Denisovan DNA, and this in fact helps them to adapt to living at high altitudes.

What is also interesting is that whereas Andean Highlanders in South America have adapted to high altitudes by having more oxygen-carrying haemoglobin in their blood, Tibetans have adapted by having less haemoglobin in their blood.

Scientists generally believe that the Neanderthal and Denisovan genes survived in Europeans and Asians because these genes were useful health-wise for the climatic and environmental conditions that these populations were living in.

The presence of Denisovan genes in Melanesian peoples is not something to be embarrassed about. It is a simple recognition of the fact that, like Neanderthal genes in Europeans and Asians, these Denisovan genes helped Melanesian ancestors to survive and flourish.

Maybe I could blame my bad teeth on some Neanderthal gene!

Some interesting links:

https://www.sciencemag.org/news/2014/07/tibetans-inherited-high-altitude-gene-ancient-human
https://www.sciencemag.org/news/2019/03/our-mysterious-cousins-denisovans-may-have-mated-modern-humans-recently-15000-years-ago

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