On this week’s episode of The Insight I discussed the field of cultural evolution with Richard McElreath. The author of Mathematical Models of Social Evolution, he was in a good place to explain why the field is relatively formal. This is in contrast for example to modern American cultural anthropology. Basically, formality keeps you honest and allows you to be wrong. Verbal arguments are amenable to subtle and not so subtle updating so as to dodge the acceptance that a model is false nearly indefinitely. Words are just imprecise enough that miscommunication can creep into the discourse.
I thought of this while reading The First Farmers of Europe: An Evolutionary Perspective. This book outlines the latest results from a variety of fields and refutes once and for all one particular mathematical model of how agriculture spread to Europe. I am alluding here to the “wave of advance” model for the spread of agriculture in Europe (most forcefully pushed by Albert Ammerman and L. L. Cavalli-Sforza). The general idea here is that farming spread through demographic increase and the diffusion of the excess population as a particular region achieved its carrying capacity. Like R. A. Fisher’s ambition to make evolutionary genetics as regular as the laws of thermodynamics, the proponents of this viewpoint were attempting to reduce a complex cultural process down to a few parameters.
And certainly, it was a useful null model in its time.
While a wave of advance should proceed gradually and continuously, the reality as outlined in The First Farmers of Europe is that farming expanded in Europe is a discontinuous manner. Both spatially, and temporally. Instead of an expanding wave, diluting its genetic signal through admixture in all directions, what ancient DNA and archaeology seem to indicate to us is that early European farmers expanding from the southeastern fringe of the continent into Central Europe (LBK) as well as across the Mediterranean (the Cardial Culture) were very particular about where they settled. The LBK in Central Europe were the first farmers of the region, and close examination of their settlement patterns suggests that they were dense agglomerations in areas characterized by loess soils. Vast swaths of territory remained forested, likely inhabited by Mesolithic hunter-gatherers. Additionally, the expansion of the LBK was not gradual. Rather, they expanded rapidly from the edge of the northern Balkans, where the boundary between agriculturalists and hunter-gatherers had remained static.
This illustrates a general principle: cultural change is often discontinuous, punctuated. Stephen Jay Gould asserted that “stasis” of biological forms were maintained through some form of balancing selection. I think the reality is that stasis culturally is much more empirically supportable, and it’s due to the human tendency to conform and follow group norms and traditions. It took decades for Central and Eastern European farmers to take up potato cultivation, despite the fact that their soils and climate made this an ideal crop. Farmers are simply conservative.
But, culture can go through periods of rapid change and equilibration. Why? Though external exogenous forces, like climate change, might trigger the initial steps, ultimately a set of endogenous factors might result in a rapid shift from one state to another. The Roman adoption of Christianity as the state religion. Or the radical change in mores in the West between 1965 and 1970. And, the emergence of the LBK cultural complex and its rapid expansion in a few centuries from northern France to Poland.
The First Farmers of Europe relies heavily on ancient DNA to clarify the demographic character of particular cultures, but its archaeological focus means that the author resolves the mechanism by which particular dynamics in the ancient DNA literature came about. For example, between the early and middle Neolithic period in Northern Europe, the fraction of Mesolithic hunter-gatherer ancestry amongst farmers increased from less than 10% to nearly 30-40% in some areas. What happened here? It seems the early intensive farming techniques gave way more extensive patterns of subsistence, which resulted in the encroachment of agriculturalists on territories inhabited by hunter-gatherers, and the ultimate absorption of the latter by the former.
There is a lot of specific detail that is fascinating in The First Farmers of Europe . In particular, through deep exploration of the arrival of farming to the British Isles the narrative illustrates the boom-bust cycles that characterized early agriculturalists within Europe. Early Neolithic farmers in Britain and Ireland, likely descended from populations with more affinity to the Cardial Culture than the LBK, shifted from wheat, to barley, to agro-pastoralism. This is down the ladder of per unit of land productivity. Barley is more resilient than wheat, but a less productive crop. This indicates that their lifestyle was fundamentally not sustainable, and the late stages of Neolithic British culture were defined by lower population densities and greater mobility than earlier periods. The rise of Stonehenge is coincident with the shift to agro-pastoralism, but the phenomenon of “henges” seems to issue from the far northern region of Scotland and the Orkneys, which retained a higher density and more complex social systems longer than other regions of the archipelago.
We know now that this fallen world ended with the arrival of the Beaker Culture ~2500 BC. Genetically it seems that the dominant signal that you see in the modern British Isles dates to this period, with only a small proportion derived from the Neolithic people, let alone Mesolithic hunter-gatherers. I suspect that the Beaker Culture is associated with the arrival of Celtic languages in the British Isles. And, I suspect that the mythos preserved by people such as the Irish may then be associated with events and happenings in the transition from the Neolithic to the Copper Age. Though the people who built Stonehenge were superseded, we know that their successors repurposed the site for themselves. The former people and their creations were likely not forgotten. I believe, for example, that the legends of the Tuatha de Danann preserve elements of contact between the later Neolithic peoples and the incoming Beaker Culture. The Tuatha de Danann are in fact associated in legend with sites which date to the Neolithic.
Clearly, we are reaching the end of the road in general insights for how agriculture spread to most of Europe. By and large, it was through migration. It did not occur through mass action of individual actors continuously and gradually through reproduction. Rather, it spread in fits and starts, and in the early period was highly localized with a patchy distribution. How general are these insights to other parts of the world? I suspect that we’ll see similar dynamics elsewhere.
As details get fleshed out, archaeology needs to be synthesized with other fields such as myth. The closing of one intellectual frontier will result in the opening of others.