The recognition and subsequent detection of the importance of teosinte introgression in the racial diversity and heterotic gene architecture of maize has been one of the outstanding achievements of Paul C. Mangelsdorf’s investigations into the origin of maize. This paper documents three areas in Mexico and Guatemala where maize and teosinte hybridize and where there is a system by which native cultivators exploit the heterotic nature of maize to increase their harvest. There is little reason to doubt that the hybridization and subsequent introgression of teosinte genes into maize observed at these sites is changed from that which has occurred over the past three thousand years resulting in the tremendous diversity and pronounced hybrid vigor in maize.