Because animal cells keep dividing over an organism’s life, and each division carries the risk of producing a cancerous mutation, it should follow that larger animals with longer life spans are at higher risk of developing cancer. Not for elephants, whose 5500-kilogram bodies have startlingly low rates of cancer, a fact that has puzzled scientists for decades. According to a study published yesterday in Cell Reports, researchers discovered that elephants have extra copies of two cancer-fighting genes: P53, which hunts for cells with miscopied DNA, and LIF6, which obliterates the mutated cells before they can form a tumor. When researchers checked the evolutionary record, they found that LIF6 became inactive in elephant DNA millions of years ago, and then mysteriously came back to life, The New York Times reports. The researchers hope to use the results to find new ways to treat cancer in humans.