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 epoch 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 correlates strongly with human migration. In North America, for example, the arrival of Clovis hunters around 13,000 years ago coincides with the rapid disappearance of nearly 35 genera of large mammals. Second, archaeological evidence supports human predation: kill sites with spear points embedded in megafaunal bones have been found on multiple continents, indicating that humans actively hunted these animals. Finally, ecological modeling suggests that even modest human hunting pressure could drive slow-reproducing megafauna to extinction. Large mammals typically have long gestation periods and small litter sizes, making their populations highly vulnerable to additional mortality. Thus, human overhunting, not climate change or other natural causes, was the primary driver of this mass extinction.

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The reading's argument that human overhunting caused megafaunal extinction is flawed. First, the timing correlation is not as strong as claimed. In many regions, such as South America and Australia, megafaunal extinctions occurred before or after human arrival, with gaps of thousands of years. For instance, in Australia, humans arrived around 50,000 years ago, but many large species persisted until 20,000 years later, which contradicts a simple overhunting scenario. Second, the archaeological evidence for hunting is extremely rare. Only a handful of kill sites exist worldwide, and many so-called 'kill sites' are actually scavenging events or natural deaths. If humans had driven these animals to extinction, we would expect far more abundant and widespread evidence of hunting, similar to the massive bone deposits found at later bison kill sites. Finally, the ecological model used in the reading ignores the role of climate change. At the end of the Pleistocene, rapid warming and shifts in vegetation dramatically altered habitats. Many megafauna were adapted to cold, open environments, and as forests expanded, their food sources declined. Climate-driven habitat loss alone could explain the extinction, without invoking human hunting. Therefore, the reading's overemphasis on human causation is unwarranted.