In this undated photo made available by the journal Nature on Tuesday, September 30, 2014, monarch butterflies cluster together as they spend winter in Mexico. The butterflies are famous for migrating from the U.S. and Canada to Mexico for the winter. A study by researcher Marcus Kronforst of the University of Chicago released in the journal Nature on Wednesday, October 1, 2014 suggests the species itself also started out in North America some 2 million years ago, instead of South or Central America. (Photo by Jaap de Roode/AP Photo/Nature)
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