Great news for anyone still feeling guilty about our race's bloody extirpation of woolly mammoths, mastodons, giant sloths, and bear-size beavers. Turns out, it wasn't us. The real culprits, says researcher Dale Guthrie with the University of Alaska, were moose, as well as bison and elk, whose migration from Asia coincided with climate and habitat changes that favored them over large ice-age grazers. Some scientists, of course, will still put the blame on a race of hunters known as the Clovis people. But now at least, we have a legitimate out.