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BOB HIRSHON (HOST):

What killed the big beasts? I’m Bob Hirshon and this is Science Update.

Until about 12,000 years ago, lions, mammoths, and even giant, eight-foot-long beavers roamed North America. Then they went extinct. Humans were just becoming established in North America, and many scientists blame them for the extinctions. But the warming climate also could have doomed the big mammals. A study in the Journal Nature finds that both were to blame.  Researchers found that some mammals went extinct despite having no contact with man, while others had smaller populations caused by the warm climate but were pushed to extinction by human hunters.

In other news, in the Journal of Visualized Experiments, scientists report that swimming sea creatures have a big effect on global climate. Billions of waggling fish, jetting squid and flapping jellyfish mix warm and cool water to such an extant that it changes climate patterns. I’m Bob Hirshon, for AAAS, the science society.