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Agriculture has no single, simple origin. A wide variety of plants and animals have been independently domesticated at different times and in numerous places. The first agriculture appears to have developed at the closing of the last Pleistocene glacial period, or Ice Age (about 11,700 years ago). At that time temperatures warmed, glaciers melted, sea levels rose, and ecosystems throughout the world reorganized. The changes were more dramatic in temperate regions than in the tropics.
Although global climate change played a role in the development of agriculture, it does not account for the complex and diverse cultural responses that ensued, the specific timing of the appearance of agricultural communities in different regions, or the specific regional impact of climate change on local environments. By studying populations that did not develop intensive agriculture or certain cultigens, such as wheat and rice, archaeologists narrow the search for causes. For instance, Australian Aborigines and many of the Native American peoples of western North America developed complex methods to manage diverse sets of plants and animals, often including (but not limited to) cultivation. These practices may be representative of activities common in some parts of the world before 15,000 years ago.
Plant and animal management was and is a familiar concept within hunting and gathering cultures, but it took on new dimensions as natural selection and mutation produced phenotypes that were increasingly reliant upon people. Because some resource management practices, such as intensively tending nondomesticated nut-bearing trees, bridge the boundary between foraging and farming, archaeologists investigating agricultural origins generally frame their work in terms of a continuum of subsistence practices.
Notably, agriculture does not appear to have developed in particularly impoverished settings; domestication does not seem to have been a response to food scarcity or deprivation. In fact, quite the opposite appears to be the case. It was once thought that human population pressure was a significant factor in the process, but research indicated by the late 20th century that populations rose significantly only after people had established food production. Instead, it is thought that—at least initially—the new animals and plants that were developed through domestication may have helped to maintain ways of life that emphasized hunting and gathering by providing insurance in lean seasons. When considered in terms of food management, dogs may have been initially domesticated as hunting companions, while meat and milk could be obtained more reliably from herds of sheep, goats, reindeer, or cattle than from their wild counterparts or other game animals. Domestication made resource planning a more predictable exercise in regions that combined extreme seasonal variation and rich natural resource abundance.