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So Did or Did We Not Interbreed with Neandertals? August 26, 2011

Posted by Nina Rosenstand in Nina Rosenstand's Posts, Philosophy of Human Nature, Science.
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Back on the perch, folks–time for a new season of occasional insights or at least sharing of interesting stories from the web!

Only last week I watched another show in a long line of mocumentaries/supposedly nonfictional shows with a good deal of play-acting about Neandertals and early humans, the Cro-Magnons. I’m a sucker for those. I love to see human actors in some kind of crude make-up depicting the latest ideas of what our closest relatives ever on this planet may have looked and acted like. I also love to see the scientists act in front of the camera, in fairly minimal make-up. But I was surprised to see that the scientists interviewed came down massively against the idea that there might be Neandertal DNA in the human gene pool—after all, in 2010, after the Neandertal genome was decoded, researcher at the Max Planck Institite Svante Paabo was quoted as saying that 1-4 percent of genetic material in the human population that left African around 60,000 years ago came from sexual encounters with Neandertals. So why the categorical denial? Of course it could have been a dated show, but my impression was that it was recent. The fact that the show was centered around renowned paleoanthropologist Ian Tattersall could have had something to do with it—he has, for years, argued that (1) there is in all likelihood no genetic connection between living humans and Neandertals, and (2) Neandertals probably couldn’t speak or even think rationally because they lacked symbolic thinking. (The fact that crude jewelry has been found among Neandertal remains apparently hasn’t been enough to change his mind, although philosophically I’d have to say that deliberately adorning oneself with body art/ornaments shows some kind of symbolic thought, and their brain and throat structures do not exclude the power of speech.) Otherwise the show had interesting moments, such as floating the theory that perhaps Cro-Magnons didn’t actually exterminate the Neandertals by force, but by transferring diseases to them to which they had no immunity, much like it happened to the American Indian population in the 19th century.

And then we have the news, now quoted and tweeted all over cyberspace, that it seems that we—at least the descendants of those who migrated out of Africa—have Neandertal DNA in our genes after all! And it may have helped us become the extraordinarily successful species that we are (at least in the short term–who knows how long we’ll last?) by adding an immunity boost to our constitution. That, and possible interbreeding with that mysterious new-found Siberian hominin species the Denisovans may have secured our survival:

Indeed, DNA inherited from Neanderthals and newly discovered hominids dubbed the Denisovans has contributed to key types of immune genes still present among populations in Europe, Asia and Oceania. And scientists speculate that these gene variants must have been highly beneficial to modern humans, helping them thrive as they migrated throughout the world.

This DNA has had “a very profound functional impact in the immune systems of modern humans,” said study first author Laurent Abi-Rached, a postdoctoral researcher in the lab of senior author Peter Parham of the Stanford University School of Medicine.

From the analysis, the scientists estimated, for example, that more than half of the genetic variants in one HLA gene in Europeans could be traced to Neanderthal or Denisovan DNA. For Asians, that proportion was more than 70%; in people from Papua New Guinea, it was as much as 95%.

“We expected we’d see some, but the extent that these contributed to the modern [genomes] is stunning,” Abi-Rached said of the findings, released Thursday by the journal Science.

Though the researchers haven’t proved it, the vast reach of these gene variants in people today suggests that they probably gave some early modern humans an advantage over others, he said.

Our ancestors’ HLA systems may have been perfectly tailored for Africa but naive to bacteria, viruses and parasites that existed in Europe or Asia, rendering them susceptible to disease.

Mating and mixing their genomes with those of their Neanderthal and Denisovan relatives could have been a speedy way to set up their immune systems to combat new, unencountered threats.

What is philosophically interesting from the point of view of speculations about human nature (philosophical anthropology) is not so much whether we slept with Neandertals or not. My own hunch is that we did interbreed and created viable offspring, but like I posted in an earlier blog entry, it was probably because of hunters raping women of the other species rather than nice, romantic interspecies marriages. What is philosophically interesting is our reaction to these theories: Why is it so important for some people to see it verified that we didn’t interbreed? And what makes it so vital for others that we did? I’m not saying that the scientists work out theories that fit their preferred view, but many laypeople (such as myself) who follow these stories have usually taken sides. Can this be boiled down to on the one hand a wish to keep human nature separate and special, and on the other hand a wish to see us closely related to all life on this planet? Competing visions of exclusivity vs. inclusivity? And where will such visions take us? Just remember Kennewick Man and the battle over his origins: Was he an early European, an American Indian ancestor, or perhaps a visitor from Asia? Each explanation carries its own political slant. Ask yourself, in your heart, would you rather that humans who migrated out of Africa were distantly related to Neandertals, or would you rather they/we weren’t? And then ask yourself, Why?



1. Paul J. Moloney - August 28, 2011

According to biological definition, subspecies can interbreed and have fertile offspring. The supposed DNA findings seem to indicate that this is what happened. An essential characteristic of being human is the capacity to reason, even if that capacity is impeded in someway, e.g., by brain damage. If this is true then the Neandertals must have had some capacity to reason, or, otherwise, they could not have been a subspecies. Still, there had to be some difference between humans and Neanderthals or they would be the same species. The difference could have been in the power of reason, or it could have been some other minor difference or both. The Neandertals could have had a more limited power of reason, which is the impression I get, whether that impression is true or not. This is speculation on my part. Not only is it speculation on my part but it is speculation on theory, which means that it is speculation on speculation. It is a very nebulous activity indeed to speculate philosophically on anthropological theories!

If humans and Neandertals were subspecies then they had to be more specifically the same than specifically different. Since humans have been on their own for so long, at least according to our limited personal experience, it may be difficult, if not impossible, to imagine another species of humans. Also, some people may think of Neandertals more as animals than as human, even though humans are animals, which could make the very thought of interbreeding repugnant.

2. thereviewer - August 29, 2011

Very good post. Detailed, accurate and thought-provoking. I love how the subject as a sub-topic of science captures everyone as we can all relate to the stories. They involve us. And yes, I like to believe that we do have Neanderthal DNA within our genome. Here is how I broke the initial news story back in 2010: http://jkendrickensis.wordpress.com/2011/07/07/how-neanderthal-are-you/

3. Nina Rosenstand - September 5, 2011

Thanks, reviewer. And here’s the latest: additional evidence that ancient humans interbred with other species–but this time there seem to be haplotypes (DNA sequences) from a third, extinct unknown hominin species:

4. forrest noble - September 8, 2011

Fun subject Nina 🙂

If modern humans and Neanderthals lived together in some of the same areas for many thousands of years, as much evidence suggests, there is no doubt in my mind that there would have been some mixing of genetics since there seems to be little doubt that they could interbreed.

The question, I believe, is whether the evidence is clear that Neanderthal DNA can be tagged in modern human genomes. Some say it can be observed in nuclear DNA, others say mitochondrial DNA, and others again say there is no conclusive evidence of either.

Whether 1-4% as some have suggested concerning nuclear DNA, or just in mitochondrial DNA as others have proposed, most, like myself, would probably bet a pretty penny that there is at least some of it there 🙂

It is also fun, as Nina suggests, that there might be motivations for some people to believe one way or the other when the evidence may be debatable 🙂

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