The most complete sequence of the development of agriculture is given by the Tehuacan Archaeological-Botanical Project, of which the field work was done in 1961 and 1962 by a team under R. S. MacNeish, which has studied the Tehuacan Valley in Puebla from the beginning of human occupation, about 9000 B.C., to the Spanish Conquest. We are only concerned with the first part, up to about 2000 B.C., by which time cultivated plants contributed more than a quarter of the food supply. The area was chosen because it was a promising region to search for wild maize, and what was believed to be wild maize was indeed found there, although the claim has since been disputed. At any rate maize was improved as time went on, and other plants were domesticated or introduced from other regions, a phenomenon which can be illustrated by the sequence previously studied in NE Mexico. At the same time, population gradually increased and permanent settlements developed.