The earliest domesticated pigs in Europe, which many archaeologists believed to be descended from European wild boar, were actually introduced from the Middle East by Stone Age farmers, new research suggests.
The research by an international team led by archaeologists at Durham University, which is published recently in the journal Proceedings of the National Academies of Sciences, analysed mitochondrial DNA from ancient and modern pig remains. Its findings also suggest that the migration of an expanding Middle Eastern population, who brought their 'farming package' of domesticated plants, animals and distinctive pottery styles with them, actually 'kickstarted' the local domestication of the European wild boar.
From the article, it doesn't specify why the researchers think it was people hauling the pigs and not just the pigs being traded around. I thought this part was interesting:
"The domestic pigs that were derived from the European wild boar must have been considered vastly superior to those originally from Middle East, though at this point we have no idea why. In fact, the European domestic pigs were so successful that over the next several thousand years they spread across the continent and even back into the Middle East where they overtook the indigenous domestic pigs. For whatever reason, European pigs were the must have farm animal."
I did quite a bit of reading up on pigs in the Middle East for this paper and recall some slight memory tickles regarding pig origins.
UPDATE: Paper here from 2000 (free!) on other work.