The Extinction of the Megafauna: A Climate-Driven Event
Around 50,000 to 10,000 years ago, many large terrestrial animals—such as woolly mammoths, giant ground sloths, and saber-toothed cats—disappeared from the fossil record. While some scientists argue that human hunting played a central role, a closer examination of the evidence suggests that climate change was the primary driver of these extinctions. First, the timing of the extinctions correlates strongly with major climatic shifts, not with human arrival. In North America, for example, the last glacial maximum ended about 20,000 years ago, and the subsequent warming and drying led to rapid habitat loss. The megafauna, which were adapted to cold, stable environments, could not cope with these changes, and their populations declined well before humans became widespread. Second, many megafauna species had survived previous human contact on other continents, such as Africa and Asia, where humans had existed for hundreds of thousands of years. If hunting were the main cause, these populations would have been extinguished long ago, but they persisted until the late Pleistocene. This suggests that the unique climatic conditions of the late Pleistocene, not human predation, were the decisive factor. Third, paleontological data show that megafauna populations were already in decline due to vegetation shifts. Pollen records indicate that grasslands and tundra, which provided food for herbivores, were replaced by forests and shrublands as temperatures rose. This reduction in food supply would have led to malnutrition and lowered reproductive rates, ultimately driving species to extinction. Therefore, the megafauna extinctions are best explained by climate-driven environmental changes rather than human overhunting.
🎧 听力讲座
🎯 模拟考试环境：先点「播放讲座」听完内容，再作答。听力原文默认隐藏。
Now listen to part of a lecture on the topic.
Professor: The reading argues that climate change, not human hunting, caused the megafauna extinctions. However, this view is flawed. First, the timing argument is misleading. While climatic shifts did occur, the final extinction events in many regions, such as North America and Australia, coincide precisely with the arrival of human hunters, not with the most severe climate changes. In fact, megafauna survived many earlier glacial-interglacial cycles, which had similar or even more dramatic climate swings, without going extinct. So climate alone cannot explain why they died out only when humans appeared. Second, the claim about Africa and Asia is incorrect. In those continents, megafauna coexisted with humans for a long time, but they evolved alongside hominins, developing fear and avoidance behaviors. When humans reached new continents like the Americas, the animals had no such adaptations and were easy prey. This is why extinctions followed human arrival almost immediately, while African species persisted. Third, the vegetation change argument is not supported by evidence. Pollen records show that grasslands and open habitats remained widespread in many areas until the very end of the Pleistocene. Moreover, climate models indicate that the warming and drying would have actually increased grassland productivity in some regions, providing more food, not less. The real cause of population decline was overhunting, which reduced herbivore numbers and subsequently affected predators. Human hunting, not climate, was the decisive factor in these extinctions.
📝 写作提示 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
