Planet Earth

The great northern culture war

Gene ExpressionBy Razib KhanDec 3, 2010 6:58 PM


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A new paper in The New Journal of Physics shows that a relatively simple mathematical model can explain the rate of expansion of agriculture across Europe, Anisotropic dispersion, space competition and the slowdown of the Neolithic transition:

The front speed of the Neolithic (farmer) spread in Europe decreased as it reached Northern latitudes, where the Mesolithic (hunter-gatherer) population density was higher. Here, we describe a reaction–diffusion model with (i) an anisotropic dispersion kernel depending on the Mesolithic population density gradient and (ii) a modified population growth equation. Both effects are related to the space available for the Neolithic population. The model is able to explain the slowdown of the Neolithic front as observed from archaeological data

The paper is open access, so if you want more of this:

Just click through above. Rather, I am curious more about their nice visualization of the archaeological data:

Note how much variance there is in terms of the rate of change of the clines. As I've observed before there was a "break out" of the LBK farmers into Central Europe nearly 7,000 years ago, but it took much longer to close the gap between the farms on the frontier and the sea. This is well known from the archaeology, as there seems to have been a pause of ~1,000 years across much of the north European plain. On the scale of 10,000 years that's not much time, but that's about 40 generations. In Frisia it looks like the spreading of farming stopped for nearly ~2000 years! Why the abatement of the spread of farming? I think the authors of the above paper are correct in their acceptance of the conventional wisdom of greater Mesolithic densities in Northern Europe. But I think perhaps a better description might be maritime Northern Europe. We often imagine early farmers displacing hunters and gatherers of game and herb, but what if in much of the world the main clash numerically was between dense populations oriented toward the sea, and those who were depended on the land? About seven years ago a study came out which argued for a rapid transition from seafood to meat in the diets of early Britons, Why Did Ancient Britons Stop Eating Fish?:

When cattle, sheep, pigs, and wheat arrived on the shores of Great Britain about 5,000 years ago, fish quickly fell off the Neolithic menu, according to an analysis of human bones scattered throughout the island. ... "Farming really took off in Britain during the Neolithic. The main questions concerning the speed of change relates to how quickly Mesolithic peoples adapted—or otherwise—to the new farming methods and/or the spread of farming into Britain by new farming communities," he said. The research by Richards and colleagues Rick Schulting at Queen's University Belfast and Robert Hedges at the University of Oxford tracks the shift in diet by examining the dietary signature stored in the bones. They find that the shift was rapid and complete at the onset of the Neolithic. "Marine foods, for whatever reason, seem to have been comprehensively abandoned," the researchers conclude in the September 25 issue of the journalNature. ... "We determined that after the introduction of domesticates, as well as the other artifacts associated with the Neolithic, the isotope values showed that marine foods were not used anymore," he said. "We then infer that this is a switch from wild foods such as fish and shellfish to the new domesticates that arrive at this time." ... Richards said there are three plausible reasons why the British abandoned seafood from the beginning of the Neolithic: the domesticated plants and animals presented a steady source of food; the shift was forced by a climate change; or cultural pressure.

In the early 2000s the idea of wholesale rapid demographic replacement was not in the air. I think we need to put that back on the table. Here is the chart on isotope ratios from the 2003 paper:

Notice the sharp discontinuity. Richards et al. in 2003 interpreted this as a rapid cultural acquisition of the Neolithic lifestyle ~2500-3000 BC. They note in the media reports that later Britons, for example at the time of the Roman conquest, seem to have utilized fish a bit more in their diet than these early Neolithics. This stands to reason, much of Britain is not too far from the sea. To me the very sharp drop in marine consumption is indicative more of a food taboo, than a practical shift. Obviously farmers would primarily be subsistent on grain, but there's no necessary reason to avoid meat or fish, but as it happens in many parts of the world societies preserve and perpetuate exactly such norms. These norms may have spread through cultural diffusion, for example through an adoption of a new religion. Or, the norms may have been brought by a new group which arrived in large numbers and replaced the indigenous population. Here is an equivalent chart from Denmark from an earlier paper by the same group:

When we think of peoples who aren't farmers, we often think of marginalized nomadic or semi-nomadic groups. Many of the remaining hunter-gatherers such as Bushmen, as well societies which supplement their conventional lifestyle with a lot of hunting & gathering, such as the indigenous peoples of Siberia or the Sami of northern Scandinavia, occupy territory which is simply not viable for conventional agriculture. But this was not so in the past. Before the farmers arrived the rich bottom-lands were occupied by hunters & gatherers, of fish, game, grain, and nuts. In certain ecologies, such as around productive estuaries one could imagine enormous aggregations of these peoples. Additionally, it seems likely that a sedentary lifestyle predates farming. A good contemporary analog for what ancient Northern Europe may have been like was the Pacific Northwest before the European settlement. These native tribes were relatively affluent because of the abundance of salmon runs, and engaged in lavish signalling, such as with their famous potlatches. Seeing as how there are Atlantic salmon runs in places like Norway and Scotland one can make even closer correspondences perhaps!

As I have stated before just because we have no written records of this period, we can not assume that these were necessarily the fragmented and scattered "small-scale societies" which we're familiar with today. There may have been ideologically motivated political coalitions and alliances which broke down along ethnic and cultural lines. In the paper above the authors argue that there is evidence that a climatic constraint, crops which do not have a good yield in cooler or warmer temperatures, is a weak hypothesis. If so I wonder if it is a bit too pat to simply model the dynamics as a diffusive "bottom up" process. Seems plausible enough for much of Europe where Mesolithic populations were thin on the ground because of local carrying capacity, but I suspect that the encounter between dense agglomerations of farmers and fishermen resulted in an inevitable ramp up of political integration and consolidation, as villages and tribes had to coordinate together because of a positive feedback loop of conflict. Image Credit: Lordkinbote, Mactographer

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