You might be interested in this in depth article about Mexican corn evolution and the Monsanto's GMO monster corn.
http://www.thenation.com/article/36330/retreat-subsistenceHere is an excerpt:
"To this day, indigenous farmers continue to comb their fields for successful plants with useful characteristics, saving their seeds and exchanging them with neighbors. This process is central to indigenous culture in Mexico, and through continuous breeding indigenous agriculturists have internalized and accelerated the process of not just crop domestication but also plant evolution. In the Mexican countryside there are fifty-nine corn "landraces," distinct cultivars that have been carefully developed over millenniums by indigenous farmers for different attributes: growth at high altitudes, early or late maturation, the ability to withstand drought or heavy rain and utility for particular dishes or shamanic rituals.
Mexico's landrace corn is consumed locally, but because it benefits from 9,000 years of breeding for diverse conditions, it represents a reservoir of genetic adaptability that many consider essential to the future of the world's commercial corn crop. Kathleen McAfee, a political economist at San Francisco State University, observed that Mexican landraces "may even prove vital in the future to the continued productivity of corn farming worldwide, given that new traits must be continuously added to maize and other crops as crop pests evolve and climatic conditions change."
This is a very long read but a very interesting article.