 According to the most widely held evolutionary model, the crop was derived directly from "Z. m. parviglumis" by selection of key mutations; but in some varieties up to 20% of its genetic material came from "Z. m. mexicana" through introgression.All but the Nicaraguan species of teosinte may grow in or very near corn fields, providing opportunities for introgression between teosinte and maize.First, and later-generation hybrids are often found in the fields, but the rate of gene exchange is quite low.