Revealed by a Multidisciplinary Effort: History of Maize Domestication Not What We Thought: The domestication of maize, a process which began in what is now central Mexico nearly 9,000 years ago, was far more complex and nuanced than once previously thought, a new study finds. The results of an analysis of the ancient grain's genetic heritage reveals southwestern Amazonia as a secondary improvement center for early maize. The findings provide new insight into the human-mediated evolutionary processes that gave rise to one of the planet's most important staple crops. In a related Perspective, Melinda Zeder writes: "The remarkable new multiproxy study of the dispersal of maize into and across northern South America is a fine example of recent advances in unraveling the complex histories of early domesticates." Domesticated maize evolved from teosinte, a wild grass of Mexico, and rapidly spread through the Americas, filling early agricultural landscapes and becoming a near-ubiquitous food source by the time of European arrival. While its widely understood that maize domestication occurred once, the nature of its domestication and spread into South America remain unclear and existing archaeological and genomic data do not always agree. Logan Kistler and colleagues sequenced the genomes of maize from South America - both domesticated indigenous varieties as well as archaeological samples of ancient corn - and compared them to the genetic lineages of modern and ancient maize and teosinte worldwide. According to Kistler et al., the results suggest that ancestral maize arrived in South America "semi-domesticated." Isolated from their Mexican progenitors before the genetic hallmarks of domestication could be fixed, distinct South American lineages evolved -- some becoming fully domesticated under continued human selection. Combining their genomic findings with archaeological, paleoecological and linguistic data, the authors suggest that this parallel, yet independent secondary improvement likely began in the southwestern Amazon.