The white egg yolk at left, seen next to a yellow yolk, may seem strange, but it's just a result of the chicken feed used, scientists say. Junko Kimura/Getty Images hide caption

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President Obama applauds as former first lady Barbara Bush and former President George W. Bush help President George H.W. Bush stand at the opening ceremony of the George W. Bush Presidential Library on April 25 in Dallas. Former first lady Laura Bush looks on. Kevork Djansezian/Getty Images hide caption

itoggle caption Kevork Djansezian/Getty Images