Abstract
Using a database with the mitochondrial DNA (mtDNA) of 513 Neolithic individuals, we quantify the space-time variation of the frequency of haplogroup K, previously proposed as a relevant Neolithic marker. We compare these data to simulations, based on a mathematical model in which a Neolithic population spreads from Syria to Anatolia and Europe, possibly interbreeding with Mesolithic individuals (who lack haplogroup K) and/or teaching farming to them. Both the data and the simulations show that the percentage of haplogroup K (%K) decreases with increasing distance from Syria and that, in each region, the %K tends to decrease with increasing time after the arrival of farming. Both the model and the data display a local minimum of the genetic cline, and for the same Neolithic regional culture (Sweden). Comparing the observed ancient cline of haplogroup K to the simulation results reveals that about 98% of farmers were not involved in interbreeding neither acculturation (cultural diffusion). Therefore, cultural diffusion involved only a tiny fraction (about 2%) of farmers and, in this sense, the most relevant process in the spread of the Neolithic in Europe was demic diffusion (i.e., the dispersal of farmers), as opposed to cultural diffusion (i.e., the incorporation of hunter-gatherers).
Highlights
The Neolithic transition was a major transformation that introduced agricultural economics, radically changed the environment, and led to increased population densities and new forms of social organization[1, 2]
If clinal patterns are not observed in analyses based on principal components, admixture, f3, f4, D-statistics, etc., the reason is that those analyses are based on many markers but, as explained above, the spatial distribution of each one can be due to other processes in addition cultural diffusion
In order to study the existence of a genetic cline for haplogroup K in early Neolithic populations and subsequently compare it to our simulations, we have gathered all mitochondrial DNA (mtDNA) information of Early and Middle Neolithic individuals reported in the literature, and we have grouped the data into regional cultures according to their location, date and reported culture (Supplementary Data S1)
Summary
The Neolithic transition was a major transformation that introduced agricultural economics, radically changed the environment, and led to increased population densities and new forms of social organization[1, 2]. Clearly the frequencies of different genetic markers have different spatiotemporal dependencies, because they are due to different processes For this reason, in order to estimate the percentage of farmers involved in cultural diffusion we should not to include many arbitrary markers (as in genome-wide studies). A totally independent reason why genome-wide studies cannot determine quantitatively the percentage of farmers involved in cultural diffusion is that, e.g., Mathieson et al.[6] assume only two source populations, namely an Anatolian Neolithic one and Western HGs, and use f4-statistics to estimate, e.g., a 93% of Anatolian Neolithic ancestry and a 7% of Western HG ancestry for Early Neolithic farmers in Germany. Haplogroup K satisfies condition (1) above, in contrast to other potential Neolithic markers (N1a, T2, J, HV, V, W, and X)
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