Thorin, We Hardly Knew Ye

Humans – that is to say, homo sapiens – have been fascinated by the Neanderthals since they were first identified in 1856. For many years, they were thought to be the original cave dwellers, leading a brutish, animal-like existence sometime in the distant past. Over the years, and especially with the advent of DNA as a tool, we’ve learned that were quite possibly were as intelligent as modern humans, they used tools, they buried their dead, and they even practiced dentistry,  Not only that, they not only overlapped with modern humans but also interbred with us; we have an estimated 1-4% of their DNA even today.

 

You're not likely to run into a Neanderthal, but wouldn't it be cool? Credit: Microsoft Designer

And yet the mysteries continue.

A new paper in Nature sheds some new light on the genetic data from Neanderthals, using the DNA from 27 individuals across ten sites and dating back some 50,000 years. Although the species apparently died out within 10,000 years from then – a blink of the eye in the evolutionary timescale -- these individuals seemed to be healthy and well-connected to other Neanderthal populations.

It had long been speculated that humans essentially drove Neanderthals to extinction, outcompeting them and forcing their populations to small enough sizes that they became inbred and unsustainable. This research does not support that thesis.

“Until now, we only had four high-quality Neanderthal genomes and a limited number of lower-quality ones, so most questions about the regional diversity of Neanderthals have been difficult to address,” said lead author Alba Bossoms Mesa, a doctoral researcher at the Max Planck Institute for Evolutionary Anthropology. “By generating genetic data from multiple individuals from the region of present-day Belgium and France, we can now examine late Neanderthal populations in much greater detail.”

Neandertal skeletal elements from the Spy 1 and 2 skeletons (Lohest Collection, 1886) from Spy Cave in Belgium. © P. Semal, Royal Belgian Institute of Natural Sciences, CC-BY 4.0

UCLA computational geneticist Benjamin Peter, who is one of the paper’s corresponding authors. added: “In other, earlier Neanderthal populations, close relatives were interbreeding, leading to unhealthy levels of genetic diversity similar to what we see today in some endangered species. But this population in Belgium and France does not seem to be dying out, even though we know that they will die out in the end.”

That’s not even the most surprising finding. Professor Peter says: “I think the most interesting finding we made is that these Neanderthals are genetically relatively healthy, with no strong signs that there was inbreeding depression. It’s also interesting that we didn’t find evidence that they have ancestry from anatomically modern humans, even though we know that at least they must have overlapped in time.”  

It gets even more interesting. Dr. Blossoms Mesa notes: “Our results add to a striking asymmetry. We repeatedly find Neandertal ancestry in early modern humans, but so far, we have not found clear evidence of recent modern human ancestry in late Neandertals."

Perhaps modern human men didn’t find Neanderthal women attractive (or vice-versa), perhaps Neanderthals were too formidable for humans to approach, or perhaps homo sapiens-Neanderthal babies didn’t survive. I like to think that homo sapiens women found the Neanderthal tough guy image irresistible, while Neanderthal women found our men to be, well, kind of wimpy. Or perhaps homo sapiens women were more likely to wander alone, where they might meet a Neanderthal man. We’ll never know.

Or perhaps we may yet gain more insight. Co-author Marie Soressi, Professor of Hominin Diversity Archaeology at Leiden University, says: “We are only beginning to uncover the diversity and complexity of Neanderthal populations. As more genomes become available from sites across Europe and beyond, we can move from studying isolated individuals to reconstructing entire communities, their relationships, and the social networks that connected them.”

"This study highlights the power of ancient DNA to reveal variation within Neandertals on a much finer scale than was previously possible," says co-author Janet Kelso, a group leader at the Max Planck Institute for Evolutionary Anthropology. "Rather than viewing late Neandertals as a single declining population, we are beginning to recognise a more complex picture of regional diversity, connectivity, and population history."

Illustrating that complex picture, I can’t help thinking about a finding from a couple years ago, the so-called Thorin (no, not the dwarf from “the Hobbit”). He was a Neanderthal who was part of a unique lineage that existed in Europe for some 50,000 years. 

“Until now, the story has been that at the time of the extinction there was just one Neanderthal population that was genetically homogeneous, but now we know that there were at least two populations present at that time,” said first author and population geneticist Tharsika Vimala of the University of Copenhagen.

That’s not the most surprising thing. The real surprise, as co-first author and discoverer of Thorin Ludovic Slimak of the Center for Anthropobiology and Genomics of Toulouse, France, told LiveScience: "The population of Thorin had spent 50 millennia without exchanging a single gene with the classical Neanderthal populations."

He further noted: “50,000 years of divergences is what separates the tiny dog of your grandma from a wolf.” It’s a long time to be genetically isolated. 

Speaking to IFLScience, senior author of the study Martin Sikora of the University of Copenhagen alternatively puts it like this: “The divergence between Thorin and the other Late Neanderthals is comparable to all modern humans out-of-Africa. As we all know the wide phenotypic diversity of modern humans, I would expect similar diversity among Neanderthal populations.” 

This was not like the Aboriginals in Australia being separated for other humans for tens of thousands of years due to geographical isolation. There were plenty of other Neanderthals around Thorin’s people. They apparently just chose not to mingle, or weren’t curious enough to find other humans.

Professor Slimak expressed his surprise: “We thus have 50 millennia during which two Neanderthal populations, living about ten days' walk from each other, coexisted while completely ignoring each other. This would be unimaginable for a Sapiens and reveals that Neanderthals must have biologically conceived our world very differently from us Sapiens.”

Keep in mind, that around this time, not only were there homo sapiens and Neanderthals, but also Denisovans, homo luzonensis, and homo floresiensis, although not all of them lived in exactly the same places or at exactly the same times. Still, think of the swap meets, not to mention the dating options.

Humans didn’t drive all of the great apes (e.g., orangutans, gorillas, chimpanzees, and bonobos) to extinction, nor all “intelligent” species (e.g., dolphins or octopuses), so it is an evolutionary mystery why it happened with other types of humans. Maybe they got a sense of what we were going to do to the world and wanted no part of it.