Explaining the Spread of Agriculture into Europe

The practice of growing food and keeping livestock was invented numerous times throughout the world. One ‘center’ of agriculture is said to be the Middle East. Despite the fact that calling the Middle East a “center” in this context is a gross oversimplification, it is true that agriculture was practiced in Anatolia and the Levant for quite some time before it was practiced in Europe, and it seems that the practice more or less spread from the middle east across Europe over a fairly long period of time.

ResearchBlogging.orgArchaeologists have long asked the question: Was this a spread of agricultural people, or the spread of the practice of agriculture, or, even, the independent invention of agriculture by various groups independent of earlier manifestations of this practice elsewhere?

The earliest archaeologists made simple claims of population movements and conquest, and it was easy for them to see Indo Europeans marching across the landscape displacing the local hunter-gatherers. Later, there were shifts in the way archaeological problems were conceived and dealt with which made diffusional, and especially conquest-based models impossible to sustain politically regardless of any merit they may have had. During this period, strong arguments were made against diffusion.

One thing we see during this period of time is the shift in head shape from what is called dolichocephalic to what is called brachycephalic, both across time and across space. This head shape variation (seen by some as a dichotomy with intermediate forms, and by others as a continuum) was essentially a proxy for race for earlier archaeologists. It was proposed that brachycephalic people were more advanced and that they were the bearers of agriculture and other supposedly advanced practices across Europe.

Both scientifically oriented questioning of this theory, and politically motivated revisionism caused this model to eventually go away. Franz Boaz demonstrated that this variation in head shape was highly labile and likely to be an effect of environment rather than an indication of ancient racial affinity. Subsequently, over the last 10 years or so, a number of studies have been done on this topic showing that Boaz was wrong — that this is genetic — and that Boaz was right, and that it is not genetic. Other studies have indicated that it might be both, and still other studies have indicated that it could be adaptive (as opposed to random variation).

If head shape change (though conceived in a more sophisticated, or at least, obtuse, manner by modern physical anthropologists than the brachy-dolichocephalic model) is labile and environmental, then changes in craniometrics across time and space do not necessarily tell us much about the movement of people with agriculture in Europe over th last 10 thousand years. If it is adaptive or results from some environmental change, then the head shape changes could easily be explained as reactions to agriculture, and would not indicate movement of people. If the variation in craniometrics is neutral and very heritable, then it may be considered as almost unambiguous evidence of the movement of people across the landscape.

If there are enough skulls and burials, and if the association between the actual adoption (or invention) of agricultural practices and the appearance of changes in skull shape can be correlated. Which, at the moment, is tenuous at best.

Well, a new paper in PLoS ONE makes the claim that we should believe that these craniometric changes are genetic, selectively neutral, and indicate the movement of people across the landscape rather than the movement of head-changing ideas.

From the paper:

Here, we employ measurements of Mesolithic (hunter-gatherers) and Neolithic (farmers) crania from Southwest Asia and Europe to test several alternative population dispersal and hunter-farmer gene-flow models. We base our alternative hypothetical models on a null evolutionary model of isolation-by-geographic and temporal distance. Partial Mantel tests were used to assess the congruence between craniometric distance and each of the geographic model matrices, while controlling for temporal distance. Our results demonstrate that the craniometric data fit a model of continuous dispersal of people (and their genes) from Southwest Asia to Europe significantly better than a null model of cultural diffusion.

Therefore, this study does not support the assertion that farming in Europe solely involved the adoption of technologies and ideas from Southwest Asia by indigenous Mesolithic hunter-gatherers. Moreover, the results highlight the utility of craniometric data for assessing patterns of past population dispersal and gene flow.

Our null model of cultural diffusion allows for admixture between Mesolithic and Neolithic populations living contemporaneously under a model of isolation-by-distance. However, the results show that it is more likely that the arrival of farming in Europe was accompanied by the active dispersal of people from SW Asia, which created a barrier to gene flow between hunters and farmers during the period of co-existence. We, therefore, do not rule out some gene flow between hunters and farmers but argue that the craniometric data does not support strong admixture between Neolithic and Mesolithic populations.

Plausible. The paper does not cite the most important critique of the genetic proposal for craniometric variation. Furthermore, my gut feeling is that of the half dozen papers that have come out over the last ten years on this issue, I could have predicted the conclusion by knowing the authors name rather than looking at the authors’ analysis a little more than I would like. There are no identified genes affecting head shape in the ways postulated. I personally have no problem with people moving, and I think the shift away from the movement of people during the 1960s, 70s, ad 80s was absurd in archaeological studies. Nonetheless, I have similarly cynical feelings about head shape. To me, the jury on this one is still out.

The paper is published in an Open Access journal, so you can read it for yourself!

Pinhasi, R., & von Cramon-Taubadel, N. (2009). Craniometric Data Supports Demic Diffusion Model for the Spread of Agriculture into Europe PLoS ONE, 4 (8) DOI: 10.1371/journal.pone.0006747

Gravlee, C., Bernard, H., & Leonard, W. (2003). Heredity, Environment, and Cranial Form: A Reanalysis of Boas’s Immigrant Data American Anthropologist, 105 (1), 125-138 DOI: 10.1525/aa.2003.105.1.125

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0 thoughts on “Explaining the Spread of Agriculture into Europe

  1. I’m not in a position to express an opinion on the papers, but this summer, I was struck by the similarity of pre-industrial farms tools on display in a folk musuem in Galacia, Spain and anything I’ve seen in the US. The exhibits were labeled in Galician, which in writing is not similar enough to the Spanish I learned in school to make much head way in reading the labels. However, after a childhood spent going to historical museums, restored homes, and living history museums, I was pretty sure I could identify most of the items.

  2. I’m decidedly long-headed, to the point that comfortable stetsons can be a bit of a challenge to find.
    Perhaps that’s why I have lately been wondering if the criteria by which we identify “agriculture” in the prehistoric record would pick up the signals showing that a woodland landscape that had been consistently modified with selection by humans to produce in a not-entirely naturally dispersed way. Heavily forested prehistoric Eurasia seems to be considered a sparsely populated wilderness but the forests along the Amazon River it has been suggested might have been more like a garden; being neither the wild untamed wilderness nor agriculture as it would be recognized by Eruopeans of that brief era of contact.

  3. Interesting, I’ll take a look at that paper. Without strong admixture though, wouldn’t you expect to see a dramatic reduction in genetic diversity at the point of adoption of agriculture? And I’m not aware of evidence for that, although it’s not something I follow closely. Certainly in the UK and NW Europe where agriculture came late and we have plenty of Neolithic human remains, it should be easy enough to test.

  4. Later, there were shifts in the way archaeological problems were conceived and dealt with which made diffusional, and especially conquest-based models impossible to sustain politically regardless of any merit they may have had.

    Academic PC run amok?

    When was “later”, and what events made historically-educated people refuse to contemplate invasions as a plausible model?

    Not even, e.g., Riane Eisler (who popularized mother-goddess-centered prehistoric utopia scenarios) went that far ’round the bend!

  5. Pierce, it was the New Archaeology of 1967/8 (longacre, hill, chang, early binford, ascher, etc.) The post-Childe phase. I oversimplify. But about 1968 through 1979 saw the publication of hundreds of papers putting the breaks first on migration then later, difussion. I’m sure migration was way overplayed before this period and it was probably good to get away from that, but the anti-diffusionist literature is sometimes over the top.

  6. I have long considered a scenario in which ‘replacement’ does not require displacement or conquest. It involves disease. Settled agricultural societies were breeding grounds for disease, which would have selected for resistant genotypes. Hence measles, chicken pox and influenza are relatively benign to them (us). Then, as the society expanded, it encountered non-resistant hunter-gatherers and disease eradicated them, leaving empty lebensraum for the farmers. The fate of native North Americans in the 1500s is an example of how this could happen.

    The agriculturalists may net even have noticed what they were doing.

  7. What little I’ve read on this topic seems to indicate that the process was different for different parts of Europe (slow migration from the SE up to around the Danube; selective diffusion along the coast in Southern Europe, with only some aspects of the ‘agriculture package’ being adopted.) So the answer would depend on location. I presume the studies above are for SE and Central Europe, not Italy and Spain.

  8. … it was the New Archaeology of 1967/8…

    Yeah, I had a strong hunch that this was some sort of backlash (maybe the more appropriate term would be backwash) from the US war against Vietnam.

    Though you’d think, even while the conquest itself was clearly failing, that the admixture of new genes into the population of Indochina would have been recognized (not to mention the new technologies).

    djlactin @ # 6: Settled agricultural societies were breeding grounds for disease…

    William H. McNeill’s Plagues and Peoples has a great chapter about how the culture which grew rice in paddies thereby took over all of southern China – and would have even if they’d lost every battle, just by breathing on the other guys.

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