托福综合写作

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The extinction of the megafauna—large animals such as mammoths, giant sloths, and saber-toothed cats—at the end of the Pleistocene has long puzzled scientists. While many factors have been proposed, the most compelling explanation is overhunting by early humans. First, the timing of megafaunal extinctions closely correlates with the arrival of modern humans on each continent. In North America, for example, the wave of extinctions occurred roughly 13,000 years ago, just after the Clovis culture appeared, suggesting that human hunters were the primary cause. Second, archaeological evidence supports this view: numerous kill sites have been discovered where butchered megafaunal bones are associated with spear points and other human tools. These sites demonstrate that humans actively hunted these animals, and given their slow reproductive rates, even modest hunting pressure could have driven populations to collapse. Third, the megafauna that survived the Pleistocene, such as bison and deer, are generally smaller, faster-reproducing species that could withstand hunting pressure, whereas the extinct giants were large, slow-breeding, and thus more vulnerable. This pattern strongly implicates human predation as the decisive factor, rather than climate change, which would have affected all species more uniformly.

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The reading's claim that human overhunting caused megafaunal extinction is not convincing. First, the correlation between human arrival and extinction is oversimplified. In Africa and Asia, where humans evolved and lived for hundreds of thousands of years, megafauna survived much longer, and many species still exist today, such as elephants and rhinos. If humans were such efficient hunters, why did they not drive these animals to extinction long ago? Second, the archaeological evidence is far weaker than the reading suggests. While kill sites exist, they are relatively rare and often ambiguous; some argue that many sites show animals that died of natural causes and were merely scavenged by humans. Moreover, the number of humans at that time was likely too small to have killed entire populations of giant animals across vast continents. Third, the pattern of extinction does not match human hunting preferences. Humans typically target large, slow-moving prey, yet many extinct megafauna, such as giant kangaroos in Australia, were not ideal prey, while some fast-reproducing species also went extinct. In contrast, climate change at the end of the Pleistocene was dramatic and caused rapid shifts in vegetation and habitats, which would have been catastrophic for specialized large herbivores and the carnivores that depended on them. So, the evidence points more strongly to climate and environmental factors than to human overhunting.