DNA from the cobs of ancient maize (corn) shows how the crop was taken to the US southwest from Mexico.

Credit: RS Peabody Mus. Photo by Donald. E. Hulbert

Maize was domesticated from the wild grass teosinte, an inedible weed, more than 6,000 years ago in southern Mexico, and later spread throughout the Americas. A team led by Rute da Fonseca and Thomas Gilbert at the University of Copenhagen analysed nuclear DNA from 32 maize samples from several archaeological sites spanning Mexico and the US southwest (pictured is a 5,000-year-old specimen).

They conclude that maize arrived in the US southwest around 4,000 years ago along a highland route in central Mexico — not by a Pacific coastal route as other studies had suggested. Along the way, maize evolved into a sweeter and more drought-tolerant crop.

Nature Plants http://doi.org/x6p (2015)