A new analysis of the extinction of woolly mammoths and other large mammals more than 10,000 years ago suggests that they may have fallen victim to the same type of "trophic cascade" of ecosystem disruption that scientists say is being caused today by the global decline of predators such as wolves, cougars, and sharks. The cascading events were originally begun by human disruption of ecosystems, a new study concludes, but around 15,000 years ago the problem was not the loss of a key predator, but the addition of one -- human hunters with spears.
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