The Extinction of the Megafauna: A Climate-Driven Event
During the late Pleistocene, approximately 50,000 to 10,000 years ago, many large terrestrial animals, such as woolly mammoths, saber-toothed cats, and giant ground sloths, disappeared from North America. While some scientists argue that human hunting was the primary cause, a closer examination of the evidence suggests that climate change was the dominant factor. First, the timing of these extinctions aligns closely with major climatic shifts, particularly the warming at the end of the last Ice Age. Sediment and ice core records show that temperatures rose rapidly around 15,000 years ago, leading to dramatic changes in vegetation, which would have disrupted the food supply for herbivores and, in turn, the predators that relied on them. Second, many megafauna species had survived earlier periods of human presence without going extinct. For instance, humans arrived in North America at least 20,000 years ago, yet the major extinction pulse occurred much later, suggesting that human hunting pressure was not sufficient to cause extinction. Finally, the extinction selectively affected large-bodied animals, which are more vulnerable to environmental stress due to their slower reproductive rates and greater caloric needs. This pattern is more consistent with climate-driven habitat loss than with human hunting, which would likely target a wider range of species, including smaller game.
🎧 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 same topic.
Professor: The reading presents a seemingly convincing case for climate change as the main driver of megafauna extinctions, but its arguments are flawed. First, the timing argument is misleading. While a major warming event occurred about 15,000 years ago, many megafauna, like the woolly mammoth, survived that warming and only disappeared later, during the Younger Dryas, a period of rapid cooling. Moreover, similar climate shifts had occurred repeatedly during the Pleistocene without causing massive extinctions. In contrast, the arrival of sophisticated human hunters, such as the Clovis culture, coincides precisely with the extinction pulse. Second, the claim that humans coexisted with megafauna for thousands of years ignores the fact that early human populations were small and lacked advanced hunting technology. It was only when human populations grew and developed efficient weapons, like the Clovis spear points, that hunting pressure became unsustainable. This explains why extinctions peaked after 13,000 years ago, not earlier. Finally, the selective extinction of large animals actually supports the overhunting hypothesis. Large animals are slow to reproduce and provide a large amount of meat per kill, making them prime targets for human hunters. In contrast, a climate-driven extinction would likely affect all species in a habitat, including small animals and plants, but the fossil record shows that small mammals and birds largely survived. Thus, the evidence points strongly to human activity, not climate, as the primary cause.
📝 Hướng dẫn viết Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
📊 TOEFL Integrated Writing Rubric
Content Accuracy: Accurately capture the relationship between lecture and reading
Information Completeness: Cover all key counter-arguments from the lecture
Structure & Coherence: Logical organization and progression
Language Use: Grammar, vocabulary, expression accuracy
Scored 0-30 based on holistic scoring (original 0-5, scaled to 30).
