The Ghosts of the European Pleistocene

2011’s Cave of Forgotten Dreams was a strange film. I went to watch it in the theaters mostly to see the paintings of Pleistocene peoples in an immersive manner, but the director and narrator, Werner Herzog, used the film as an instrument to forward his thesis that humanity as we understand it emerged during this period in the European Ice Age.

Whether he knew it or not Herzog was channeling the “Great Leap Forward” model of the origin of our species. That in an almost punctuated manner the cultural proteanism which we take to be a defining hallmark of our species emerged at some point deep in what we call the Ice Age. In The Dawn of Human Culture Richard Klein localized this burst of humanity ~50,000 years ago in Africa, and hypothesized that it was triggered by a biological change which enabled language fluency. In The Humans Who Went Extinct Clive Finlayson posits that cultural changes associated with the Gravettian people in central Eurasia eventually defined what he meant to be human, and explained the marginalization of Neanderthals.

To a rough approximation I’m skeptical of both these models. I don’t think humanity emerged fully formed like Athena over the last 50,000 years. Rather, humanity we understand humanity is deeply primal, and a feature of the root of our lineage, millions of years in the past. If Homo erectus populations were still around they deserve all the rights of humans, despite their numerous differences.

I suspect that we’ll found out that ‘behavioral modernity’ is a cocktail of soft selection on standing variation and cumulative cultural change. But that doesn’t mean that the Pleistocene history of Europe is not important or interesting. And recently we’ve obtained enough ancient DNA to sketch out a general picture of demographic, if not cultural, change.

Everyone should read The genetic history of Ice Age Europe. But I suspect the impact is going to get deeper when more archaeologists are familiar with the implications. Here is the abstract:

Modern humans arrived in Europe ~45,000 years ago, but little is known about their genetic composition before the start of farming ~8,500 years ago. We analyze genome-wide data from 51 Eurasians from ~45,000-7,000 years ago. Over this time, the proportion of Neanderthal DNA decreased from 3–6% to around 2%, consistent with natural selection against Neanderthal variants in modern humans. Whereas the earliest modern humans in Europe did not contribute substantially to present-day Europeans, all individuals between ~37,000 and ~14,000 years ago descended from a single founder population which forms part of the ancestry of present-day Europeans. A ~35,000 year old individual from northwest Europe represents an early branch of this founder population which was then displaced across a broad region, before reappearing in southwest Europe during the Ice Age ~19,000 years ago. During the major warming period after ~14,000 years ago, a new genetic component related to present-day Near Easterners appears in Europe. These results document how population turnover and migration have been recurring themes of European pre-history.

I modified the model of demographic turnover to the left, adding labels for the primary paleoanthropological cultural groups. Instead of starting with the archaeology the authors let the genetic results guide them. What they discover is that there were roughly four turnovers in population defined by four “clusters”:

– the first Europeans who succeeded the Neanderthals, who seem to have left no descendents

– the Goyet cluster, associated with Aurignacians

– the Vestonice cluster is associated with the Gravettians

– the El Miron cluster with the Gravettians

– the Villabruna cluster with various late Pleistocene cultures, and is the direct ancestor of Mesolithic hunter-gatherers present in Europe when the first farmers arrived

A quick calculation suggests that very little of the ancestry of modern Europeans has deep roots across much of the continent going back to before the Last Glacial Maximum ~20,000 years ago. The “Pleistocene” ancestry of Europeans mostly derives from the last group, the Villabruna cluster. In the paper the authors note that this group is unique for several reasons:

– some individuals in this cluster have an affinity with East Asians (earlier Pleistocene groups do not)

– more universally, individuals in the Villabruna cluster have a notable affinity with Middle Eastern populations which was not evident in earlier Pleistocene clusters

Recall Middle Eastern populations can be modeled as a mix of a West Eurasian group similar to European hunter-gatherers, and, “Basal Eurasians,” who are an outgroup to all non-Africans (European hunter-gatherers to Oceanians to Amerindians!). The authors posit that the gene flow is more likely from the Middle East, because earlier European clusters have affinities with Villabruna, but they share nothing with the Middle East. The Villabruna cluster does not have Basal Eurasian ancestry though. So we might be looking at complex population structure.

Two general issues that crop up in this paper are sampling limitations and population expansions into Europe from the east. The disappearance of Goyet ancestry, only to reappear as part of the El Miron cluster, is curious. Perhaps the post-Goyet people occupied ecologies less likely to be fossilized? It reminds us of the resurgence of hunter-gatherer ancestry in Europe of the Middle Neolithic. As for why there seems to be an eastern bias into intrusive populations into Europe, these groups may simply have had a larger population, and so been more likely to avoid meta-population extinction events?

Finally, the authors point out that Gravettian culture in Siberia and Europe does not seem to be genetically related. This suggests that these people were very modern, because a hallmark of the modernity is that ideas can move between groups without too much genetic exchange.

Europe has the best coverage of ancient DNA. What we find here are repeated population turnovers and a lot of complexity and contingency. Is Europe peculiar? There is circumstantial evidence from modern DNA that Australians are descendants of first settlers. And to some extent this is also true in the case of East Asians if the work reported out of the Fu lab holds up. South Asians though are more likely to be like Europeans, and Middle Easterners show some of the same dynamics during the Holocene.