By AD 1500, when Europeans began to explore and colonize other continents, agriculture had expanded extensively in all the habitable continents except Australia (which remained a land of hunter-gatherers until the 18th century), and most of the world’s population of some 350 million obtained almost all their food from agricultural products. But the systems of crop and livestock production that had gradually evolved in the core regions of early agriculture still retained much of their biotic and dietary distinctiveness. European expansion brought about the worldwide, especially transoceanic, dispersal of crops and domestic animals (see columbian exchange), and as subsistence agriculture increasingly gave way to large-scale commercial production geared to international trade, the cultivation of many minor crops declined, with accordant loss of dietary diversity. This process was driven particularly by the development of monocultural systems of production, notably plantation agriculture of tropical crops such as banana and sugar cane (both of SE Asian origin) in tropical America, and cacao (from C. America) in W. Africa. Similarly, large-scale ranching and mechanized grain farming developed in N. America following the introduction of cattle and wheat (of SW Asian origin).