The Extinction of the Megafauna: A Climate-Driven Event
During the late Pleistocene, roughly 50,000 to 10,000 years ago, many large terrestrial mammals, such as woolly mammoths, saber-toothed cats, and giant ground sloths, disappeared. While some scientists attribute this extinction to human hunting, a closer examination suggests that climate change was the primary driver. First, the timing of these extinctions correlates strongly with major climatic shifts, not with human arrival. For instance, in North America, the last glacial maximum ended about 18,000 years ago, and most megafauna disappeared during the subsequent warming period, which brought dramatic habitat changes. Second, climate change caused significant alterations in vegetation, disrupting the food sources of these large herbivores. As temperatures rose, vast grasslands and tundra were replaced by forests, reducing the open habitats that supported herds of mammoths and horses. Third, many megafauna species had survived earlier human contact in Africa and Asia, where hominids had existed for hundreds of thousands of years, yet they did not go extinct until the climate shifts of the Pleistocene-Holocene transition. This indicates that human hunting alone was insufficient to cause their demise; rather, environmental stress from climate change was the decisive factor.
🎧 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 a lecture on the same topic, challenging the points in the reading.
Professor: The reading argues that climate change, not human hunting, drove the megafauna extinctions. However, that view is flawed. First, the timing argument is misleading. While climate shifts occurred, the extinctions did not always coincide with them. In Australia, megafauna disappeared around 46,000 years ago, shortly after human arrival, but before any major climatic change—the climate was stable then. Similarly, in New Zealand, large birds like moas went extinct only 700 years ago, during a period of minimal climate variation, right after Polynesian settlers arrived. Second, the claim about vegetation changes is not supported by data from many regions. In Siberia, pollen records show that mammoths had access to nutritious grasses until very late, yet they vanished around 4,000 years ago, after humans had spread there. In fact, some megafauna thrived in forested environments, so forest expansion cannot explain their extinction. Third, the reading’s point about Africa and Asia is misleading. In those regions, megafauna had co-evolved with hominids for millions of years, developing fear of humans. But when modern humans reached new continents, like the Americas, the animals had no such fear and were easy prey. This explains why extinctions were rapid and severe in the Americas but less so in Africa. Thus, human predation, not climate, best explains the pattern.
📝 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).
