Scientists have settled that maize was domesticated about 9,000 years ago in the lowlands of Mexico from a subspecies of teosinte called parviglumis. In a paper published in Science, a team of geneticists reported that maize has a second wild ancestor, a highland subspecies of teosinte called mexicana.
The team from the United States, China, and Mexico led by researchers at the University of California Davis analyzed the genomes of more than 1,000 samples of maize and wild relatives and found that about 20 percent of existing maize varieties worldwide come from mexicana, which hybridized with maize some 4,000 years after people first domesticated the plant.
These findings indicate that while maize was domesticated around 10,000 years ago, it was not until 4,000 years later when it hybridized with highland teosinte, that maize became a popular crop and food staple. This finding is also supported by archaeological evidence of the increasing importance of maize during the same time.