Research by UMaine researcher Dan Sandweiss places cornmeal on the menu for native Americans much earlier than previously believed. Working with colleagues from Ithaca College and the Smithsonian's National Museum of Natural History, Sandweiss discovered evidence of cultivated corn in the Cotahuasi Valley of southern Peru that dates back to nearly 4,000 years before the present, suggesting that corn was an important crop in that region more than 1,000 years earlier than previously thought.
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2006:
https://www.academia.edu/3838610/Early_maize_agriculture_and_interzonal_interaction_in_southern_Peru