While lots of labels tout their lack of genetically modified ingredients, if California's Prop. 37 succeeds, foods containing GMOs would have to be labeled. Paul Sakuma/AP hide caption

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Paul Sakuma/AP

Italian farmer Giorgio Fidenato picks up what's left of his genetically altered corn after anti-GMO activists trampled it, back in 2010. Paolo Giovannini/AP hide caption

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Paolo Giovannini/AP