The appearance of genetically modified proteins in maize seed stocks throughout Mexico paints a curious pattern that suggests why efforts to prevent the flow of transgenic plant material into that country could fail, reports a team of researchers in Mexico and at the University of California, Davis. The researchers hope that their findings, published May 29 online in the journal Public Library of Science, will help guide development of methods and public policies for regulating the movement of genetically modified plant material into local seed stocks in centers of crop origin and diversity.