It is commonly known that the plight of endangered species today is both large and pressing. However, many people do not realize that humans began causing the extinction of organisms starting a long, long time ago.
At the end of the Pleistocene epoch (12,000 years ago), about two-thirds of the existing large mammal species in North America suddenly disappeared, including species of mammoths, camels, sloths, and saber-toothed cats. Similar losses occurred on the other continents at roughly the same time. This sudden, great dying happened at the same time as the arrival of the first humans in the Western Hemisphere. Scientists think today that there are so few animals weighing over one hundred pounds because so many were killed ages ago. In Madagascar, for example, a giant flightless bird and a dwarf hippopotamus disappeared soon after Homo sapiens arrived. No other global climactic or geographical factors could explain the extinctions. Then, a few hundred years 
ago, direct exploitation by humans, habitat destruction, and predation by foreign mammals wiped out the Dodo bird of Mauritius Island. The large animals were especially vulnerable in northern America, where they had little time to adjust to the sudden appearance of man.
Direct Causes - Overexploitation
