It is believed that the majority of the breeds we now know are descended from the Eurasian Wild Boar (Sus scrofa). Archaeological evidence from the Middle East indicates domestication of the pig occurs as early as 9,000 years ago, with some evidence for domestication even earlier in China. Figurines, as well as bones, dating to the sixth and seventh millennia BC have been found at sites in the Middle East. Pigs were also a popular subject for statuettes in ancient Persia.

From here the pig card across Asia, Europe and Africa. One interesting point, while most livestock where utilized initially by nomadic peoples, swine are more indicative of a settled farming community. The reason for this is simply because pigs are difficult to herd and move for long distances. Pigs have become vital to the economy in parts of the world. For example, there exists a "pig culture" in New Guinea as strong and complex as any African culture based on cattle.

http://www.ansi.okstate.edu/breeds/swine/