The Oasis Theory (or Propinquity Theory) is a core concept in archaeology, referring to one of the main hypotheses about the origins of agriculture. First put forward by V.G. Childe in his 1928 book, "The Most Ancient Near-East", the oasis theory argues that the reason people starting living in settlements was because during a dry spell, the only livable place was near oases.
The enforced clustering of humans, animals, and plants led to the domestication of all three, or so the theory goes. Another important scholar for this discussion was Robert Braidwood, who introduced the Fertile Crescent as a location of this enormous step forward (or backward, depending on your point of view).
Lots of details on the domestication of various animals and plants have been collected here.
Braidwood, Robert J., et al. 1974 Beginnings of Village-Farming Communities in Southeastern Turkey--1972. Proceedings of the National Academy of Sciences 71(2):568-572. Free download
Childe, V.G. 1969 New Light on the Most Ancient East. Norton & Company. The second edition, which can be had for a song these days.
Pluciennik, Mark and Marek Zvelbil. 2007. pp. 467-486 in Handbook of Archaeological Theories, R. Alexander Bentley, Herbert D.G. Maschner and Christopher Chippindale, eds. Altamira Press, Lanham, Maryland. A great resource for modern concepts of the origins of agriculture.
This glossary entry is part of the Dictionary of Archaeology.