Mammoth extinction: blame plants

Some scientists blame the migration of humans across the Bering Strait land bridge and their blitzkrieg form of hunting. But the picture may be far more complex, suggests University of Alaska biologist R. Dale Guthrie — at least in his part of the world. An examination of plant and pollen remains show that the region’s plant population changed dramatically between 13,500 and 11,500 years ago, affecting the kinds of food available for grazers.

Dr. Guthrie says that a “unique tide of resource abundance” was created by a shift in climate from the icy Pleistocene to the warmer Holocene. This shift in plant life, which preceded human settlement, favored some large mammals at the expense of others.

Using new radiocarbon dates for signature species such as mammoths, horses, elk, moose, and bison, as well as for human settlement in Alaska and the Yukon, Guthrie found that mammoths and horses already had declined sharply by the time humans put down roots. Meanwhile, bison, elk, and moose were thriving before humans settled in the region. The results appear in Thursday’s issue of the journal Nature.