DNA Insights into Neanderthal Society

These days, the human race comprises a single species - Homo sapiens. But until about 40,000 years ago, we shared the planet with a related but distinct group called the Neanderthals. They were so similar to us that the two groups periodically interbred, which is reflected in the fact that two or three per cent of the DNA in the average person today is Neanderthal. The reason we know this is that scientists can read and rebuild the genetic code present in ancient remains. And now there’s been an incredible discovery. The remains of a Neanderthal community in two caves in Siberia has opened a window into this world for the first time. Chris Smith asked Trinity College Dublin’s Lara Cassidy, who specialises in reading ancient genomes and wrote a commentary on the new discovery, to explain what’s been found…

Lara - This is really big news because we've never had data like this before. The authors have sequenced ancient genomes from Neanderthal remains in Siberia. Neanderthals are a sister species to our own species. Homo sapiens, they were living in Europe and surrounding areas around 40,000 years ago. They have managed to sequence 13 Neanderthal genomes. What's really special about this is that they're all coming from in and around the same time and the same place. And that allows us to explore relationships between these individuals.

Chris - Where did they study these ancient peoples then? When you say there's lots of them together, it does add a huge amount of data - it nearly doubles the number of specimens we've now got genomes on, doesn't it? But where did they all come from?

Lara - These individuals are coming from archaeological excavations in the Altai foothills in Siberia, where we have two nearby caves, Chagyrskya cave and Okladnikov. What they think is that at least some of the individuals they sequenced were contemporary, so they lived at the same time really incredibly. They found a father and daughter pair and they also found second degree relatives like an aunt and a nephew or a grandchild and a grandparent.

Chris - Were these individuals buried there then? Is that why they happen to have this grouping and they're closely related both in space and time or were they wiped out by something? Do we know?

Lara - We don't quite understand why their remains ended up in this cave. The cave itself was a campsite. They were processing bison. They'd go down, hunt bison and bring the remains back to a cave. They were also making tools to do that work.

Chris - And have we got dates from the local stratigraphy, the layers, to tell us roughly when those people were doing this?

Lara - The layers of activity are dated to between 59 and 51,000 years ago.

Chris - What does this enable us to infer about Neanderthal society, then? Because this is a special case. We've got a large group who are closely related. they're all living together. This is almost like a community. So what can we infer about the community and society in Neanderthal times from these DNA codes?

Lara - I suppose there's two conclusions this study drew. The first one was that all of the individuals they could test, they had high levels of background inbreeding. Quite extreme. I think the closest modern day comparison would be what we see for mountain gorillas. Mountain gorillas are an endangered species. Historically there's been fewer than a thousand individuals in the wild and they live in quite small community groups. Maybe 20 or so individuals are Chagyrskya Neanderthals. They're looking like there's similar demographic dynamics going on. They're living in in fairly small communities. So that's very interesting because I suppose we compare that then to our own species, homo sapiens. One of the things we're very interested in is how we differ from Neanderthals because those differences might tell us something about our own species evolution, why our own societies were so successful in terms of dispersing across the globe. Well, the Neanderthals fizzled out. They don't maybe seem as well connected to one another as modern day hunter gatherer societies that we have now

Chris - It won't have escaped the attention of listeners that that time that you're talking about is not far upstream of when this particular lineage went extinct. Neanderthals disappeared about 10,000 years after this. So could it be this is already them in decline or could it be that they disappeared because of this sort of thing - this inbreeding?

Lara - Neanderthals lineage first starts to emerge about 400,000 years ago. So they were survivors in that way. They were in Europe for a long time and they went through a lot of harsh climactic downturns and then re-expanded again. So I would say there isn't a reason to think that this type of population size is a sign of their imminent demise. This is a very debated thing about why Neanderthals disappeared. But I think the most popular theories at the moment are more of a demographic one. That they were just simply swamped by homo sapiens.

Chris - And what was the other point? Because you said there were two key learning points in this. One was this small population size. What was the other?

Lara - It also seems there is a migration between communities, but the authors proposed that this is primarily females dispersing. So leaving the group from which they were born and moving to a new community.

Chris - Is that because the males are going off and getting wives? Or is it that the women are on the move and joining other communities? Is there anything that we can learn from modern anatomically modern human societies where there are similar practices?

Lara - Yep. We can't say the exact dynamics. We don't know how similar Neanderthal social organisation was to our own. So we wouldn't want to project too much from what we see today in modern hunter gatherer societies onto a different species of human. Another thing we can look towards is our closest living relatives, which are the African apes. African apes do show female bias in dispersal. Females move between groups more than men. Some people have used that to argue that this female bias dispersal was the ancestral state. That's why actually trying to jump back in time with ancient genomes and understand what was happening in other species of humans is so important. We still don't know how flexible Neanderthals were. Maybe if we sampled another community from a different time, from a different place, they'd show male biased dispersal.