The origin and evolution of maize in the American Southwest

The origin of maize (Zea mays ssp. mays) in the US Southwest remains contentious, with conflicting archaeological data supporting either coastal or highland routes of diffusion of maize into the US.
Furthermore, the genetics of adaptation to the new environmental and cultural context of the Southwest is largely uncharacterized. To address these issues, we compared nuclear DNA from 32 archaeological maize
samples spanning 6000 years of evolution to modern landraces from across Mexico. We found that the initial diffusion of maize into the Southwest at about 4000 years ago likely occurred along a highland route, followed
by gene flow from a lowland coastal maize beginning at least 2000 years ago. Our population genetic analysis also enabled us to differentiate selection during domestication for adaptation to the novel climatic and
cultural environment of the Southwest, identifying adaptation loci relevant to drought tolerance and sugar content.