November 14, 2003
About 70% of North America's large mammals, including all the horse species, became extinct between 20,000 and 10,000 years ago. The reasons for this have been controversial - some researchers blame climate change, others the human hunters newly arrived in the Americas.
The timing of the horses' disappearance, and their size change, suggests that environmental change, not humans, were to blame, says Guthrie. The horses died out about 500 years before the first evidence of human settlement in Alaska. And their disappearance coincided with a shift in vegetation from grassland to tundra, which would have reduced their food supply. We may be mistaken in looking for blanket explanations for extinctions, Guthrie concludes: each species' disappearance probably results from a unique combination of influences and history.
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