An “in-fill” framework for the expansion of peoples in Europe: beakers, beakers everywhere!

In the 1970s A. J. Ammerman and L. L. Cavalli-Sforza argued for the validity of a model of Neolithic expansion of farmers into Europe predicated on a “demic diffusion” dynamic. This is in contrast to the idea that farming spread through the diffusion of ideas, not people. The formal theory is inspired by the Fisher wave model, but empirically just imagine two populations with very different carrying capacities due to their mode of production, farmers, and hunter-gatherers. In a Malthusian framework, the farmer carrying capacity in a given area of land might be ~10× greater than that of hunter-gatherers. Starting at the same initial population, the farmers will simply breed the hunter-gatherers out of existence.

As the farmers reaching their local carrying capacity, migration outward will occur in a continuous and diffusive process. For all practical purposes, the farmers will perceive the landscape occupied by hunter-gatherers as “empty.” This is due to the fact that hunter-gatherers often engage in extensive, not intensive, exploitation of resources. In contrast, even slash and burn agriculturalists leave a much bigger ecological footprint. They swarm over the land.

The beauty of the demic diffusion process is that that it’s analytically elegant and tractable. Families or villages engaged in primary production to “fill up” a landscape through simple cultural practices which manifest on the individual scale that allow for aggregate endogenous growth. And this model underlies much of the work by Peter Bellwood in First Farmers and Colin Renfrew’s theories about the spread of Indo-European langauges. You can call it the Walder Frey theory of history.

I didn’t really think deeply about this theory because I didn’t have much empirical knowledge until I read Lawrence Keeley’s War Before Civilization. In this book, Keeley observes that the archaeological record suggests that there was violent conflict between the first farmers and hunter-gatherers in northwestern Europe, near the North Sea. He reports that there seems to have been a broad front of conflict, presumably a prehistoric “no man’s land.” Not only that, but Keeley claims that the spread of agriculture stopped for a period. The barrier between hunter-gatherer occupation and farmer territory was not permeable. Not diffusion.

As a stylized fact, the demic diffusion framework treats all farmers as interchangeable and all hunter-gatherers as interchangeable. On the face of it, we know that this is wrong. But the assumption is that to a first approximation this axiom will allow us to capture the main features of the dynamics in question. This may be a false assumption. The fact is we know that some hunting and gathering populations can engage in intensive resource extraction and remain sedentary.

Intensive hunter-gatherers

The Pacific Northwest Indian tribes of the United States of America are the best-known examples of such hunting and gathering peoples. Because of the concentrated runs of salmon, these people could remain hunter-gatherers while maintaining relatively sedentary and dense societies characterized by social stratification (e.g., they practiced slavery). As it happens, it seems that it is on the maritime fringes of Northern Europe than the hunter-gatherers flourished the longest. Agriculture took ~1,000 years to transplant itself from northern Germany to southern Scandinavia, and even then hunter-gatherer lifestyles persisted in many locales for several thousand years until the Nordic Bronze Age (and in Finland even longer).

The flip side of the variation in intensity and density of hunter-gatherers is that the early farmers were probably less efficient and intensive than later agriculturalists. And, as the Anatolian farmers pushed into Northern Europe their cultural toolkit would be less and less effective. Even assuming local dynamics of reproductive increase as the primary driver for farmer expansion, the growth parameter of the agriculturalists in comparison to the hunter-gatherers may not have been that different in many contexts.

But the second major issue is that the assumption of continuous and diffusive expansion over wide areas is probably wrong. The early Neolithic farmers may have been stateless in a modern sense, but they were almost certainly not primitive anarchies. They were pre-state polities of some sort no doubt and exhibited coordination and cultural uniformity over large distances. An illustration of what might happen to small groups of farmers is what happened to white American homesteaders who occupied territory too close to the Comanche lands. Future archaeologists may see an empirical pattern of demic diffusion of white Americans from the east to the west, but that expansion occurred only within the scaffold of a political-military superstructure.

On a fundamental level demic diffusion, and the higher reproductive value over time of farmer peoples than hunter-gatherer peoples, are essential pieces of the puzzle of the peopling of Europe during the Holocene. But they need to be framed in the context of the discontinuous expansion of cultural zones of activity and freedom for farming communities, under the umbrella of some supra-village social and political order. This step by step expansion in a piecewise fashion probably explains the “hunter-gatherer resurgence” that David Reich’s lab has found in the temporal transects within a given region. Even if socially and politically dominant within a particular region, the farming communities likely targeted the richest and most suitable lands as predicted by classical economics. The hunter-gatherer populations likely persisted in more marginal areas and only assimilated with the dominant farmers over time. The invasion dynamics locally would exhibit patchiness in the early phases, allowing for hunter-gatherer persistence.

The fundamental lower-level dynamics are those of panmictic local populations expanding over time in a continuous fashion. These can be modeled by a few parameters. The problem is that the older idea that this could be generalized over time and space is surely wrong. Rather, inter-group dynamics probably govern a lot of the coarse-scale patterns we see. Over time farmer populations always won, but “on any given day” the outcome was always in doubt.

And so it was with agriculturalist conflicts as well. This is on my mind partly because I recently reread Genetic origins of the Minoans and Mycenaeans and The Beaker Phenomenon and the Genomic Transformation of Northwest Europe. There are lots of details within these papers that are easy to miss on first or second or even third read. For example, I noticed a sample dated to between 2200 and 1900 BC (so probably 2050 BC?) from Parma in northern Italy from a Bell Beaker cultural context which has a lot of steppe ancestry. Contemporaneous samples from Iberia seem spottier in their steppe ancestry, but that’s around when it shows up in that peninsula. Similarly, steppe ancestry arrived in Greece at some time after the Neolithic but before the Bronze Age collapse.

We know that the Beaker people arrived in Britain and Ireland rather suddenly ~2500 BC, even though the earliest evidence of the canonical beakers diagnostic for this culture are found in western Iberia in ~2900 BC. The Reich group concluded, rightly I suspect, that the cultural phenomenon of the Beaker people transcended a particular socio-cultural group bounded by kinship and genetic affinity. In other words, the Beaker culture was a set of peoples, in the plural.

And yet outside of Iberia and some Mediterranean locales, The Beaker Phenomenon and the Genomic Transformation of Northwest Europe makes it clear that a genetic disruption of the local demographics occurred when the society adopted the beaker. Whereas in Central and Eastern Europe Indo-European languages probably arrived with the Corded Ware people ~2900 BC, the Beaker come to our attention somewhat later, and in fact, pushed eastward into Corded Ware territory. Though the Beaker people seem to have been the vectors for steppe ancestry in many areas of Western Europe, they generally have less of it than the Corded Ware.

The Corded Ware frontier with non-Indo-European peoples to their west, south, and north, can be thought of as a cultural innovation zone. This is historically the trend, with frontier areas producing a vigorous and cohesive, yet often innovative, identity group that can mobilize resources and engages in expansion and domination. The Zhou and Chin states in China are examples of this, as is the ascendence of Roman Emperors from the trans-Danbunian region after 200 AD. It seems entirely possible then that the explosion of Indo-European Beaker people on the West-Central European frontier occurred through cultural synthesis and transmission from non-Indo-European Western Europe of the 3rd millennium, and once this society became cohesive it expanded outward aggressively.

In sum, while genetic processes are continuous and gradual, cultural processes are often discontinuous and may exhibit a phase of fluctuating change alternating stasis (perhaps modeled by a Poisson distribution of periods of expansion against the typical stationary background state?).

Addendum: The Slavic expansion in Eastern Europe and the Balkans fits with this model. Their success both demographically and culturally was due in large part to an ability to adapt to the regression of social complexity. Slavic societies were antifragile. They degraded well. In contrast, the Latin and Greek peasantry were more reliant for their existence and cultural continuity on the Roman state. With the collapse of the Balkan limes in the last quarter of the 6th century, the East Roman Empire lost total control of its Europeans interior communications, and Constantinople, Thessaloniki and the Peloponnese remained connected through maritime means through the Imperial navy’s total control of the Aegean.

And the Slavs were not an anarchic people. Though organized around small tribes, they existed under the hegemony of the Avars, and in multiple instances seem to have coalesced under the leadership of non-Slavic peoples who provided a leadership caste before these groups were culturally assimilated. Their demic diffusion through the Balkans was only enabled through the scaffold of an expansion pastoralist ascendancy in areas heretofore dominated by the Roman state.

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6 thoughts on “An “in-fill” framework for the expansion of peoples in Europe: beakers, beakers everywhere!

  1. Whats even more interesting to me is that some groups of farmers seem to have been overtaken by very brutal and warlike hunter gatherers. The males were largely eliminated and the mixed, genetically and culturally altered farmer groups expanded in all directions.
    Those overtaken, transformed Neolithic communities seem to have been more mobile, more aggressive and cared more for livestock than crop farming.
    You are on the right track that the farmer expansion could only work on a highly organised way.
    As soon as the higher order showed signs of weakness, the smaller communities were overtaken or exterminated by foreigners or constant small wars made them weak with the foreign intrusion being just a matter of time.
    The higher the cultural level, the more functioning structures are needed. A malfunction of one part makes the whole vehicle a death machine for all its passengers in a worst case scenario.

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  2. “An illustration of what might happen to small groups of farmers is what happened to white American homesteaders who occupied territory too close to the Comanche lands.”

    The Comanche had horses, and rode them very well, an art they had learned from the Spanish. In this they were more like the Mongols than the less well equipped HGs the early agriculturalists would have meet.

    Speaking of the Mongols. I have assumed that distinction should be made between pastorialists who tend herds of domesticated animals, and pure hunter-gatherers who simply forage and hunt.

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  3. “The fact is we know that some hunting and gathering populations can engage in intensive resource extraction and remain sedentary.”

    Not really. This is a case of early anthropologists creating too few categories to capture the reality on the ground.

    What we know is that food production via fishing and exploitation of other coastal marine food sources is really a distinct category of food production from terrestrial hunting and gathering, herding and farming.

    Fishing communities such as those around the Baltic Sea, the Jomon in Japan, and the Native Americans of the Pacific Northwest, can engage in intensive resource extraction and remain sedentary, which gives them more staying power vis-a-vis farmers, especially farmers at the margins of the ecological range that their crop package can be utilized.

    There are really no examples of terrestrial hunters and gatherers doings this, except on a short term seasonal basis in prime hunting grounds.

    (There is also good anthropological data to support a distinction between premodern hoe farming societies and premodern plough farming societies:The former often leads to matrilineal cultures, the later always produces patriarchies.)

    “Slavic societies were antifragile. They degraded well.”

    Excellent observation and excellent turn of phrase.

    This is, apparently, the key to what made them so “awesome” that they expanded dramatically while other civilizations collapsed around them. An in depth analysis of the cultural features that made them antifragile would be worthwhile. The Slavs are exceptional in that almost all of the notable populations that were antifragile historically were pastoralists, while they were farmers.

    Were the cultural traits that gave their peoples an edge as society degraded an impediment to them in more favorable conditions?

    Seemingly not, as they were not culturally displaced after their expansion outside of Hungary ca. 900-1000 CE, and don’t seem to have been the subject of demic replacement anywhere that they expanded.

    Then again, maybe the secret to their expansion was pastoralist leadership at key moments that other societies lacked, and their only real cultural edge was their capacity the maintain their culture while in symbiosis with pastoralists elites. An “if you can’t beat them, join them” ethic can be very adaptive.

    Interestingly, you see this “if you can’t beat them, join them” norm frequently lauded in a lot of Japanese popular culture (a culture where this strategy allowed Japan to rebound from defeat in WWII quickly), but see it far less often in the U.S.

    Imagine a Slavic version of “Red Dawn” or “The Man in the High Castle” where the invaded people promptly surrender and then turn into passive-aggressive Vichy politicians who try to regain control politically from the inside while enduring humiliation, instead of heroically fighting back and violently resisting. I don’t know Slavic culture well enough to know if this is an accurate take on they key to their expansion, but it is an interesting one to consider.

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  4. The flip side of the variation in intensity and density of hunter-gatherers is that the early farmers were probably less efficient and intensive than later agriculturalists.

    Yes, with hindsight, it does feel like classical demic diffusion models popular in early 2000s to early 2010s overrate the degree of expansion by early agricultural and the intensity of their agricultural systems. I get the impression that they were thinking in terms of classical agrarian peasants under Iron Age states, after thousands of years of cultural evolution and specialization: very high density, tied to their fields rather than pretty mobile and almost constantly labouring to eke marginal calories out of marginal land, relatively pacified with little warfare among them and very low supplementary hunting and foraging. Those seem not so close necessarily to what early agricultural expansions and societies were like.

    It seems like actual agricultural expansions ran into barriers where population size of agriculturalists was low enough that either there was lots of technological transfer to hunter gatherer groups who were later able to expand more radically, or HG and agriculturalist groups merged and HG ancestry become a relatively significant component of population.

    I’d guess this probably also holds with the pastoralist expansion of Indo-Europeans and Uralic peoples. It seems plausible to me that the classic West Eurasian steppe expansions ran out of efficiency and demographic advantage at the eastern end of their expansion, so transferred much of their toolkit to East Eurasian foraging or agricultural peoples who spoke Transeurasian languages and then expanded in a big way. The same issues of a subsistence toolkit becoming marginal, but not before transferring a lot of material culture and ideas to other peoples who can then boom later, also hit the IE.

    Another thought might be on the transfer of Chinese millets to East European groups. Much of Eastern Europe seems pretty marginal for agriculture for a long time and dominated by nomadic societies (foraging and pastoralist). But at some point Chinese millets crossed the Eurasian steppe, and then when they did, the groups that were best placed to benefit by demographic expansion were Eastern European groups with relatively high European HG ancestry, not groups most heavily descended from early Anatolian farmers.

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  5. On the expansion of the Slavs:

    1) Comment from Hussein Al-Asadi’s “Estimating recent migration and population size surfaces: “In our results, the smallest inferred population sizes are in the Balkans and Eastern Europe more generally. This is in agreement with the signal seen by Ralph and Coop (2013); however, taken at face value, our results suggest that high PSC sharing in these regions may be due more to consistently low population densities than to historical expansions (such as the Slavic or Hunnic expansions).”.

    2) It also does seem that recent medieval adna papers have turned up some samples of Hungarian Avars and Ukrainian Scythians who seems specifically well within or quite close to specifically Slavic populations today.

    So I wonder how much the Slavic expansion will prove to be a kind of expansion of a single defined people, against how much it will be the coalescence together of lots of already Slavic like people across the Eastern European zone with a single lingua franca, and with an accompanying shift to agro-pastoralist and agrarian subsistence that ultimately increases population size (maybe influenced by some new crops drifting across from the east across the steppe?).

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  6. Matt, good point since we see similar in some ways HG-heavy populations in various areas of Bronze Age northeast Europe so far but I feel that the unified early Slavic language must have arisen from a relatively small area somewhere within those potentially similar populations and expanded rather dramatically and explosively throughout them during its historical expansion. Though those particular examples you mentioned might come from either very likely early Slavic (Slavs within the Avar realm) or potentially early Slavic (the quasi-Slavic Scythians from the central Ukraine around the Dnieper, one of the proposed proto-Slavic homelands – the Chernoles, Zarubinets which also experienced La Tene influence, Kiev area – look like forest steppe Baltic-like populations mixed with something central European that was WHG heavy. one was paternally R1b-P312 – Hallstatt influence?) contexts.

    The East German/Polish-like but not “generically Slavic” Tollense samples might be a good example of that kind of thing too though there are scenarios that would envision a movement of proto-(Balto-)Slavs from the west to the east and then back west with their historical expansion (like a horizontally reversed Corded Ware – Steppe_MLBA) so we might be dealing with a population speaking proto-(Balto-)Slavic and very related varieties throughout time in the first place.

    Right now even the Celtic or Italic expansions aren’t too well-clarified. What exact variety of “Celtic(-like?)” IE did Beaker Ireland and Iberia speak and what trace did it leave in the long-term (the very right-post-Beaker-like Basques after all experienced clear steppe autosomal and Y-DNA flow without switching in the long run)? Greek is in a better position due to definite Bronze Age attestation but we still don’t know when steppe ancestry first makes its appearance there, between 2200 and 1600 in typical views, or the exact dynamics of its spread. Even the exact events of the dominance of R1a in South Asia are still open even with the very good evidence of the Sintashta-Andronovo vector for its initial spread.

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