Chickens are descendents of the aggressive, pugnacious red jungle fowl of northern India and southern China. Gallus gallus is a member of the pheasant family or Phasianidae, a large, originally Eurasian group of birds that tend to colonize open forest or the edge between field and wood. Chickens seem to have been domesticated in the vicinity of Thailand before 7500 BCE, and arrived in the Mediterranean around 500 BCE. In the West, they were largely unpampered farmyard scavengers until the 19th-century importation of large Chinese birds created a veritable chicken-breeding craze in Europe and North America. Mass production began in the 20th century, when much of the genetic diversity in meat chickens evaporated in favor of a fast-growing cross between the broad-breasted Cornish (developed in Britain from Asian fighting stock) and the U.S. White Plymouth Rock.