humans exonerated in horse extinction?

Prehistoric Alaska once teemed with woolly mammoths, large bison, and wild horses. Then, about 10,000 to 20,000 years ago, about 70 percent of North America’s large mammal population mysteriously disappeared — including all the existing horse species. (The Americas remained horseless until the Spaniards reintroduced the animal in the 1500s.) The reasons behind this massive die-off remain controversial — some researchers believe that humans hunted the animals to extinction, others that climate changes led to their demise. R. Dale Guthrie of the University of Alaska suspects that, for horses at least, climate change may have been the culprit. He reports in the Nov. 13 Nature that before Alaskan horses went extinct, they shrank — their bones upon the eve of their disappearance (about 12,500 years ago) were up to 12 percent shorter than those of horses that lived 15,000 years earlier. The fact that horses became smaller suggests to Guthrie that environmental changes were at least partly to blame for their decline. “The present data do not suggest human overkill,” he writes.

This news brief appeared in the Random Data column of the Boston Globe’s Health/Science section on 11/18/2003.