Domestic cats have evolved as an urban scavenger from about 8000 B.C., when nomadic tribes settled into villages. Cats later were bred by religious cults and worshipped as sacred animals. The spread of domestic cats followed the pattern of urbanization. Such cats now inhabit every continent except Antarctica and most of the world's islands. Their largest populations are in urban areas, particularly warmer climates, where year-round food and shelter are available.