Maize has been a staple food for centuries. It is the most planted crop in the Mexican region. The country grows more than 42 different types of maize, each of which has several varieties whose number is estimated at more than 3,000 by the International Center for the Improvement of Maize and Wheat (CIMMYT). The characteristics of each variety depend upon soil conditions, humidity, altitude, and how cultivated. Some of the earliest evidence of maize cultivation suggests that domestication took place in several places at the same time.