The woolly mammoth, extinct for thousands of years, could be brought back to life in as little as four years thanks to a breakthrough in cloning technology. Previous efforts in the 1990s to recover nuclei in cells from the skin and muscle tissue from mammoths found in the Siberian permafrost failed because they had been too badly damaged by the extreme cold. But a technique pioneered in 2008 by Dr. Teruhiko Wakayama, of the Riken Centre for Developmental Biology, was successful in cloning a mouse from the cells of another mouse that had been frozen for 16 years.