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Polishing turds: social contexts of Neandertal coprolites

Finally we have something I've been waiting for for a while- Neandertal poo. Aside from providing journalists with various amusing headlines ("What the crap?"; "Poop scoop" etc.), this new research (open access article) is interesting on several levels. The obvious one reported in the paper is the identification of vegetal matter through chemical analysis, which is yet another neat addition to the ever-increasing stack of examples that Neandertals weren't the hyper-carnivores they were believed to be. However I think a couple of other things are equally interesting.

There has been at least one previous claim of Neandertal faeces (known when preserved in archaeological deposits as coprolites) from Lazaret, France, but these may not have been human, and analysis was limited to identifying pollen grains. While this kind of study is useful for information about the contemporary environment, it's not direct evidence of the food making up the coprolite.

The new study, led by Ainara Sistiaga, focused on two lines of evidence in analysing sediments from Middle Palaeolithic layers at El Salt, a Spanish open-air locale. I'll avoid repeating the details of the method, except to say it argues based on the presence and relative abundance of chemically-identified molecules (lipids, substances made during digestion of cholesterol, and another molecule -phytosterol- found in plants) that the soil samples analysed include human poo.  Further investigation by looking microscopically at thin-sections of soils from near these samples found actual remnants (extremely tiny) of what appears to be human-like coprolite matter.
The samples were from the upper level of a hearth,  

Contextual information for the El Salt sample. This shows incidentally the detail that layers in archaeological sites can potentially represent. The time covered however is harder to be sure of. Image: Open access from the paper linked above.

Julien Riel-Salvatore has blogged previously about the reported identification from El Salt of vegetable fats (as well as herbivore and fish residues) from stones associated with hearths. It's not clear however whether these are the same or different contexts to the faecal matter, and I can't find any publications on these residues at the moment. In terms of diet, there is increasing evidence from many different types of data and regions of Neandertals consuming plants (for example, dental calculus studies from the Near East, Belgium and Spain have showed various types of plants, including evidence that at least some was cooked prior to consumption). So in itself, this new study isn't ground-breaking, but rather a welcome addition to our understanding of their diet,

The BBC reporting on the paper included a comment from Stephen Buckley (who was involved with the calculus research), pointing out that we need to remember that our expectations of Neandertal diet should be more nuanced- they won't eat the same thing across their entire geographic range, which was huge. In this context, 50,000 years ago, southern Europe had a very different plant ecology to more northern areas, and so the opportunity to include plants in the diet may have been more limited elsewhere. However, I'd add that we also need to remember chronological variation- Germany 120,000 years ago (Neandertals had already been around for about the same time again at that point!) was another world to the steppe-tundra of 50 Ka, with warm temperatures and plants around like today, and animals including hippos and even macaques.

But I mentioned at the start of this post that I think there are other interesting aspects raised from the findings of this study. First, admittedly connected with diet, is the fact that not all the coprolites showed the same biomarker signature. This seems to be clear evidence of different foods being consumed. Having a varied diet may not sound earth-shattering, but every new fact we have about the Neandertals is hard-won, in part due to the trickiness of such an ancient archaeological record, but also because people demand such high standards of proof for allowing them to have done anything interesting. Therefore even though ideas have changed over the past decades from limiting them to scavengers of carnivore kills, to actually being skilled hunters themselves (and recognition has increased of the diversity of diet across the whole Neandertal world), so far little attention has been paid to the possibilities of dietary variation that experienced by individuals or across one group. This is despite the fact that food is recognised both in the later archaeological record, as well as primate studies, as a major resource in the negotiation and maintenance of social relationships.

Viking poo from York. Almost as cool as Neandertal poo! Image: By Linda Spashett Storye book (Own work) [CC-BY-2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons

I'm not sure if it is possible to determine whether the El Salt variation is a record of differences between individuals, perhaps reflecting life stage or social status, or is instead simply a time-averaging effect, showing that what was available to everybody changed according to availability- meat for a few weeks, then when animals were scarce, plant-based foods.  Or perhaps the other way round.
If it is recording variation between individuals who were living at El Salt at the same time, then a couple of circumstances spring to mind. Previous analysis of a juvenile Neandertal has showed a weaning pattern (remarkably similar to that currently advised by the NHS) of exclusive breastfeeding for about 7 months. This was then followed for the same amount of time by a mix of milk and solids, before breastfeeding stopped entirely (although abruptly, and therefore perhaps atypically early: see Katie Hinde's post on this research). While there is no data from that study, it's possible that a plant-rich diet may have been part of the weaning process, rather than starting young babies with still-sensitive digestive systems straight onto meat. The whole process of raising babies in Neandertals is something I've become extremely interested in since becoming a mother a few months ago, and I'll be writing about it soon. I might even start plotting some actual research!
Another alternative is that, just like in extant primates such as chimpanzees, individuals were eating different foods depending on their status within a group. This might be related to gender, age or even whether they currently were popular socially for whatever reason. Diet is highly likely another aspect of Neandertal life we shouldn't be consigning to a species-generic monochrome picture, but instead considering how we might examine the diversity of their lifeways.

But back to the pooing... The second thing that spun off in my mind when reading the paper is the location of the faecal matter in the hearth. Sistiaga is quoted in the BBC coverage as joking that the poo was unlikely to have been deposited in the fire when it was in use- common sense really. But I started thinking about this spatial aspect, although there is little further detail in the paper on the stratigraphic context. If there is only evidence for coprolites in the top layer, it implies that deposition wasn't something going on periodically during the life of the hearth, when no burning was occurring  (assuming that Neandertals didn't keep their fires burning continuously). Instead it might be that the poo was deposited specifically when the fire was properly out of use, rather than being deposited as part of habitual clearing of domestic space. Such cleaning of detritus from living areas is seen in at least one other Neandertal site: Kebara in Israel. Here there is very good spatial preservation, showing that Neandertals were creating a midden along one side of the cave wall, a practice which was maintained over time and involved some kind of clean-up of rubbish from across the living space. More recently further intriguing evidence from the same site suggests that the occupants may have maintained rubbish pits inside the cave, depositing mostly animal bones in them over long periods.
If the faeces at El Salt were put into the fire periodically, it would match this kind of domestic management seen at Kebara (assuming of course that faeces are not found across the whole site). On the other hand, if the poo deposition was only occuring during the final phase of hearth use, or after it was no longer in action, this could indicate that the occupants were performing some kind of less frequent clearing up activity, related perhaps to the seasonality of site use. Perhaps a spring/autumn clear-up when moving in to the site, or even when leaving it for another locale.

These ideas are pretty speculative given the amount of data available, but to me these aspects of how Neandertals organised their lives that are much more exciting than the bare nutritional implications of diet. It's really amazing the kinds of things we can find out about the Middle Palaeolithic, using a huge variety of analytical techniques. I think we shouldn't be afraid to widen our interpretations of these findings, with more general consideration of data-informed behavioural inferences. Otherwise all we will end up with are lists of sites and species consumed- informative on a basic level, but not the reason most people are interested in hearing about Neandertal archaeology.

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