In the arid Tehuacan Valley, abundant preserved organic materials have provided us with a detailed picture of economic development that can be broadly applied, with regional variations, to the whole of Mesoamerica.
In the early postglacial period, the valley's inhabitants moved seasonally, hunting game and gathering plants as they became available. By 7000 BC some of these plants and animals were extinct but others had taken their place.
Some resources occurred abundantly at certain seasons, allowing the valley's inhabitants to congregate, while other were scattered and had to be foraged by small bands. Transplanting these, and encouraging edible plants at the expense of others (for instance by weeding), allowed groups to stay together longer in one place: the beginning of cultivation.
Other, non-local, plants were introduced through trade, among them maize. By 1500 BC villages growing maize, beans, squashes and other plants and making pottery were established in the Tehuacan valley.
