6 million years ago, the first pigs lived in Europe and perhaps other places in the world. They were tamed 8,000 years ago during the Stone Age. Pigs were brought to North America on ships in the 1500’s from Spain and England by colonists and explorers. In the United States until the mid 1940’s, pigs were classified by percentage of fat into lard-type (more fat) and bacon-type (less fat). When shortenings and petroleum products replaced lard, farmers began raising only meat hogs.

Information from the World Book Encyclopedia, 1994. "Hog"

Some Links About the History of Pigs
http://maxpages.com/myzoo/Pigs_in_History
http://www.cyberspaceag.com/pighistory.html
http://piggiespiggiespiggies.homestead.com/history.html