Soot reveals Neanderthals lived lonely lives

Studying the day to day life of Neanderthals is difficult because we don’t have high-resolution data. But careful soot analysis changes that!


Neanderthals were similar to us in many ways, but they went extinct whilst we flourished. So obviously everyone has been digging into our differences to try and figure out why we survived. One possible candidate is our social networks, which seem to be more widespread in humans. However, the evidence for lonely Neanderthals isn’t particularly great. Might soot hold the answer?

That might seem like a rather random way to study this, so bear with me.

Stone age sites can take thousands of years to form. Each layer of the site could look like one occupation, but it’s really dozens of visits all mushed together. These are “palimpsests” and they’re a real pain when we study the day to day life of ancient people. Is this site one giant camp or lots of small ones?

But say each of those camps lit a fire. This would smudge up the wall. Then, this is covered up by natural accretions whilst the site was empty. The next group would make camp and light another fire, leaving another soot mark on top of this accretion. Over time bands of soot and accretion will form, chronicling the history of the site in high resolution. Much higher than if you just looked at the rock layers.

It’s this high-resolution history that might shed light on how lonely Neanderthals really were.

soot layers

Soot layers from cave wall

Soot barcodes

Of course, studying soot is a bit harder than that. Hence why palimpsests have remained a problem for so long. If the answer was as simple as “count smudge layers on the wall” we would probably have this problem licked by now.

So let’s return to our little example. Repeated occupations result in a build-up of soot layers on a cave. That alone wouldn’t be enough as we’d have no idea how old those smudges were. But a group of researchers working in France figured out an ingenious way around this problem. They realised that sometimes bits of cave wall fall off and is buried with the archaeology. Thus, each archaeological layer preserves its smudge history through dozens of wall fragments.

soot sequneces

Two overlapping soot sequences that can be lined up to build an even longer history

But of course, it’s even more complex than that. Each fragment only preserves a small portion of this history. So this French team had to painstakingly examine over a hundred fragments and look at the soot “barcode” preserved in each. These puzzle pieces can be lined up into one long history of the site. We do a similar thing for tree rings. 

Of course, it’s actually even more complicated than all of that. But at this point, you know enough to get the gist of the method. Build up long sequences by aligning wall fragments from archaeological layers. It’s tough and time-consuming but can ultimately provide a way more accurate view of the occupation history of a site than if you just look at rock layers.

The smudges of Grotte Mandrin

To put this method into practice this team examined soot from Grotte Mandrin. This juicy sounding cave is in South East France and was occupied by Neanderthals for the last 10,000 years of their time in the region (55 – 45 thousand years ago). Modern humans also seem to have moved in afterwards, living their intermittently until the end of the stone age.

Like many other stone age caves, archaeologists found dozens of roof fragments during excavation. Most research ignores them as they don’t really tell us anything, but this French team performed this cool new soot analysis. This built up a sequence of smudges spanning across every phase of occupation at the site.

The results are quite astonishing and really show how severe the palimpsest problem can be. The cave looks like 13 archaeological deposits. So that’s 13 occupations, right? In actual fact, most deposits actually had dozens of occupations bringing the grand total to 273! One Neanderthal layer was actually 70 visits to the cave!

Lonely Neanderthals

Interestingly, the dozens of visits to Grotte Mandrin tells us there were a lot of Neanderthals in the region. Several different Neanderthal toolkits were found, but they seem to move into the cave shortly after one another. This suggests there were several distinct groups all living very close by. Despite this, they don’t seem to have ever shared the site. Once one group moved in, the previous occupants never came back.

For instance, a group of Neanderthals making one set of technology (or several groups making that set) visited the cave at least 61 times. They were clearly big fans of the cave but never came back after another group turned up. That group (or groups) repeated this until someone else took over their cave.

Of course, we can’t rule out contact between these groups whilst they were living close together. But the fact they don’t share the site seems to be strong evidence of at least some isolation. This feeds into the contradictory data on Neanderthal loneliness.

Genetics reveals each group was small and isolated, sometimes even having to interbreed to survive. However, when more data is examined it turns out the overall Neanderthal population was large. How to reconcile the two? There were a lot of Neanderthal groups but they didn’t interact very often, resulting in isolation and this disparate data. And this does seem to be what’s going on at Grotte Mandrin. At several points in their history Neanderthal groups appear to have co-existed nearby, but never too close.

Possible family trees of the inbreeding Neanderthal

Of course, this is only one site. But maybe more soot will shed light on just what went on with the Neanderthals.

References

Vandevelde, S., Brochier, J.É., Petit, C. and Slimak, L., 2017. Establishment of occupation chronicles in Grotte Mandrin using sooted concretions: Rethinking the Middle to Upper Paleolithic transition. Journal of Human Evolution112, pp.70-78.

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