A Comparison of Y-Chromosome Variation in Sardinia and Anatolia Is More Consistent with Cultural Rather than Demic Diffusion of Agriculture

Abstract

Two alternative models have been proposed to explain the spread of agriculture in Europe during the Neolithic period. The demic diffusion model postulates the spreading of farmers from the Middle East along a Southeast to Northeast axis. Conversely, the cultural diffusion model assumes transmission of agricultural techniques without substantial movements of people. Support for the demic model derives largely from the observation of frequency gradients among some genetic variants, in particular haplogroups defined by single nucleotide polymorphisms (SNPs) in the Y-chromosome. A recent network analysis of the R-M269 Y chromosome lineage has purportedly corroborated Neolithic expansion from Anatolia, the site of diffusion of agriculture. However, the data are still controversial and the analyses so far performed are prone to a number of biases. In the present study we show that the addition of a single marker, DYSA7.2, dramatically changes the shape of the R-M269 network into a topology showing a clear Western-Eastern dichotomy not consistent with a radial diffusion of people from the Middle East. We have also assessed other Y-chromosome haplogroups proposed to be markers of the Neolithic diffusion of farmers and compared their intra-lineage variation—defined by short tandem repeats (STRs)—in Anatolia and in Sardinia, the only Western population where these lineages are present at appreciable frequencies and where there is substantial archaeological and genetic evidence of pre-Neolithic human occupation. The data indicate that Sardinia does not contain a subset of the variability present in Anatolia and that the shared variability between these populations is best explained by an earlier, pre-Neolithic dispersal of haplogroups from a common ancestral gene pool. Overall, these results are consistent with the cultural diffusion and do not support the demic model of agriculture diffusion.

Paternal Genetic History of the Basque Population of Spain

“…The majority of Anatolian R1b samples are of the Eastern European type, while those in Sardinia are predominantly Western European and belong to the Atlantic Modal Haplotype (Wilson et al 2001). In addition, this analysis estimated TMRCA for R1b ranging from 32,600 YA in Iberia (95% CI: 25,000 -80,700) to 19,600 YA in Anatolia (95% CI: 19,400 -44,400), well before the advent of agriculture (Morelli et al 2010). The discrepancy in TMRCA estimates between the two studies was attributed to the mutation rates used to estimate coalescent times.…”

Tracing the genetic origin of Europe's first farmers reveals insights into their social organization

“…Similarly, the Y chromosome distance map shows the greatest similarities to populations of the west and south Caucasus, and Sardinians (electronic supplementary material, figure S7, dataset S17), which can be explained by the high frequency of haplogroup G/G2a [55,61] in these populations. This might reflect genetic drift, caused by isolation and small effective population size after a direct gene flow from the Near East, which led to a fixation of this haplogroup [54].…”

New clues to the evolutionary history of the main European paternal lineage M269: dissection of the Y-SNP S116 in Atlantic Europe and Iberia

“…However, the authors believe that it is unlikely that an arrival to Europe of M269 during the Neolithic period has generated such a complex scenario of expansions for its sublineages, especially when genetic evidence of cultural diffusion has been found for Ychr in Anatolia 20,21 and for mtDNA in the refuge. 22 Thus, the spread of Neolithic culture would mean a lower demic movement.…”