Pleistocene Overkill
Around 11,000 years ago, near the end of the Pleistocene era (2.6 million to 11,700 years ago), most megafauna- Hlarge, mostly herbivorous (plant-eating) land animals- -went extinct in North America. Their disappearance has been the topic of much debate, but considerable evidence supports a hypothesis known as “Pleistocene overkill.” The idea is that, as humans spread across the continent, they preyed upon large herbivores, such as woolly mammoths, ground sloths, and tortoises, and wiped them out. As originally formulated by the American geoscientist Paul Martin, the large mammals were driven to extinction in a few hundred years in a massive, fast-moving event. A newer version of the hypothesis posits that the extinctions were more gradual, based on evidence that, in some areas, humans and large animals coexisted in the same habitats for long periods of time, despite hunting. However, the end result was the same: extinction of the megafauna. Large animals are more vulnerable to extinction than smaller ones because they cannot hide easily from human predators and because they reproduce quite slowly. It is possible that the large animals were also relatively unafraid of human beings, since they would have evolved for hundreds of thousands of years without humans present. In addition, there is some indication that a rapid shift in climate reduced the habitats of many of the giant herbivores, making them more vulnerable to human predation. Likewise, Australian biologist Tim Flannery suggests humans may have changed the environment through their actions, especially by increasing the frequency of fires.
