All civilizations have depended on agriculture for subsistence, with the possible exception of some early civilizations in Peru which may have depended upon maritime resources. Grain farms can result in accumulated storage and a surplus of food, particularly when people use intensive agricultural techniques such as artificial fertilization, irrigation and crop rotation. It is possible but more difficult to accumulate horticultural production, and so civilizations based on horticultural gardening have been very rare. Grain surpluses have been especially important because grain can be stored for a long time. A surplus of food permits some people to do things besides producing food for a living: early civilizations included soldiers, artisans, priests and priestesses, and other people with specialized careers. A surplus of food results in a division of labour and a more diverse range of human activity, a defining trait of civilizations. However, in some places hunter-gatherers have had access to food surpluses, such as among some of the indigenous peoples of the Pacific Northwest and perhaps during the Mesolithic Natufian culture. It is possible that food surpluses and relatively large scale social organization and division of labour predates plant and animal domestication.