Theories abound, but certainty is a lost cause.
Although cooking meat over an open fire in the outdoors was known to all cultures at one time, the niceties of digging a pit, to allow for concentrated heat and smokiness to develop was forgotten in Europe by the time the first colonists to Jamestown arrived. Following the lead of the local Indians, pit barbecue was quickly rediscovered, and has remained popular. Each region, however, has its own particularites and pecularities that make the dish individual and makes traveling fun. Throughout the Southeast, pork is the favored meat. This preference likely goes back to the colonial period, when pigs were let loose to grow fat on apples, nuts, and then captured and eaten later, saving the farmer effort and expense in sheltering and feeding the livestock.