Det var migrasjon og genflyt som førte til spredning av jordbruket i Europa, ikke kulturell utveksling


Den største revolusjonen noensinne – den neolittiske revolusjonen fascinerer. Etter titalls tusener av år som jegere begynte europeerne å leve som mer bofaste jorbrukere og hverdagen ble forandret for alltid. Forskere strider om dett er et resulat av migrasjoner eller et resultat av ren kulturell utveksling.  De nyeste resultatene bekrefter teorier om migrasjoner som den mest betydningsfulle element som bidro til spredning av jordbruket over hele Europa.

PloS: The spread of agriculture into Europe and the ancestry of the first European farmers have been subjects of debate and controversy among geneticists, archaeologists, linguists and anthropologists. Debates have centred on the extent to which the transition was associated with the active migration of people as opposed to the diffusion of cultural practices. Recent studies have shown that patterns of human cranial shape variation can be employed as a reliable proxy for the neutral genetic relationships of human populations.
Methodology/Principal Findings

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.

The debate over the origins of agriculture in Europe has mainly centred on two demographic models. The demic diffusion model (also known as the wave of advance) suggests a progressive dispersal of Southwest (SW) Asian Neolithic farmers into Europe [1]–[3]. This process involved region-specific and variable degrees of admixture between the incoming farmers and the local Mesolithic hunter-gatherers. Alternatively, a cultural diffusion model suggests that agricultural knowledge and technologies diffused from SW Asia into Europe but without a significant demographic expansion of SW Asian farmers [4], [5]. Various intermediate scenarios have also been proposed. Some suggest diffusion as the main underlying mechanism involved (e.g. [6]), while others argue that early European agriculture was developed independently by indigenous Mesolithic hunter-gatherer-forager populations with no diffusion of either knowledge or people from the core SW Asian regions [4].

The first mathematical analysis of chronometric archaeological data on early Neolithic European cultures demonstrated a southeast-northwest (SE-NW) temporal cline across Europe [1]. A re-assessment of the wave of advance model using a much larger data set and calculating the probability of various hypothetical centers of agricultural origin provided further support for the observed clinal pattern [7]. While this cline suggested that agriculture spread across Europe in a SE-NW fashion, the archaeological data alone cannot detect whether this is the outcome of a demic diffusion, cultural diffusion, or a palimpsest of complex demographic and historical processes. Subsequent genetic studies of classical allelic markers using principal components analysis (PCA) reported a similar SE-NW clinal pattern observed when plotting the major component of variation [8]. It has been demonstrated that PCA analyses of spatially correlated genetic data can produce highly structured results which are mathematical artifacts that do not necessarily reflect underlying historical migration and dispersal events [9]. However, partial correlations of classical genetic, temporal, and geographic matrices have also found support for the demic diffusion model [10] and hence imply that in this specific case, the clinal pattern is not artefactual but rather produced by demographic historical processes.

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