Where did pigs come from?

A study of pig mtDNA sequences by Greger Larson and colleagues in Science establishes that domesticated pigs originated in multiple geographic locations from different ancient wild boar populations.

The study shows that wild boars have a strong mtDNA association with their geographic locations, with an apparent origin in Island Southeast Asia. The authors contrast this with other domesticated animals, whose wild relatives do not give as good an opportunity for testing the origin of domesticated forms:

The wild progenitors of many Eurasian domesticates are either extinct [e.g., the aurochs (8) and the wild horse (10)] or have little or no phylogeographic structure [e.g., the wolf (11)]. Consequently, the broad distribution of surviving wild boar populations across the Old World provides a unique opportunity to analyze the origins of modern domestic lineages. Previous studies (3, 12) have identified three divergent clusters of Sus scrofa mitochondrial sequences, one Asian clade and two European groups, of which one consists solely of Italian wild boar. Both the Asian and European groups contain domestic breeds, yet molecular clock estimates indicate the split between the two groups significantly predates evidence for pig domestication, which suggests independent domestication events in each area from divergent wild boar lineages (3, 12).

They find that European pig breeds (excluding those with recent cross-breeding with Asian pigs) are related almost exclusively to European wild boar lineages, with little or no input from Near Eastern boars. The authors conclude that this is consistent with a domestication of European pigs within central Europe, perhaps Germany. They argue that Neolithic peoples entering Europe from West Asia either did not bring pigs with them, or that any pigs of Near Eastern origin ultimately did not become progenitors of European breeds. They also argue that the structure of the data exclude the alternative hypothesis, that European wild boars are largely derived from feral populations of pigs with origins elsewhere.

Additional pigs from other regions appear to provide evidence of several other domestication events in other areas. This includes India, Southeast Asia, possibly Italy, and China.

Also, the study finds that neither Celebes wild boars nor Taiwanese wild boars are related to those in New Guinea, Melanesia, or Polynesia, which they take as evidence against the idea that Polynesian human dispersal was a rapid movement of people out of Taiwan. There is no clear origin for the pigs from the Polynesian dispersal from extant wild boar lineages, which they suggest may indicate that a now-extinct lineage of Wallacean boars may have served as the origin, or that a longer-term human domestication of pigs from elsewhere in Island Southeast Asia may have occurred.

References:

Larson G. et al. 2005. Worldwide phylogeography of wild boar reveals multiple centers of pig domestication. Science 307(5715):1618-1621. Science Online