BODIES of extinct Ice Age mammals, such as woolly mammoths, that have been frozen in permafrost for thousands of years may contain viable sperm that could be used to bring them back from the dead, scientists said yesterday. Research has indicated that mammalian sperm can survive being frozen for much longer than was previously thought, suggesting that it could potentially be recovered from species that have died out. Several well-preserved mammoth carcasses have been found in the permafrost of Siberia, and scientists estimate that there could be millions more. Last year a Canadian team demonstrated that it was possible to...