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Archaeological evidence indicates that pig domestication had begun by ∼10500 years ago in the Near East, and mitochondrial DNA (mtDNA) suggests that pigs arrived in Europe alongside farmers ∼8500 years ago. A few thousand years after the introduction of Near Eastern pigs into Europe, however, their characteristic mtDNA signature disappeared and was replaced by haplotypes associated with the European wild boar.

This turnover could be accounted for by substantial gene flow from local European wild boars, although it is also possible that European wild boars were domesticated independently without any genetic contribution from the Near East.

An almost complete disappearance of Near Eastern ancestry

To test these hypotheses, the authors of this study collected mitochondrial DNA sequences from 2099 samples of ancient and modern pigs and 63 ancient nuclear genomes from Near East and European pigs. They found that European domestic pigs dating from 7100 to 6000 years possessed both European and Near Eastern ancestors, while later pigs had less than 4% of Near Eastern ancestry. The gene flow from European wild boar has thus resulted in the near-complete disappearance of Near Eastern ancestry.

The existence of traces of Near East ancestry thus indicate that while pigs were not independently domesticated in Europe, and that the vast majority of human-mediated selection over the past 5000 years favored the genomic fraction derived from the European wild boars, at the expense of the fraction that was selected previously by early Neolithic farmers over the first 2500 years of the domestication process.