The Extinction of the Megafauna: A Climate-Driven Catastrophe
Around 50,000 to 10,000 years ago, the Earth experienced the disappearance of many large mammals, including woolly mammoths, saber-toothed cats, and giant ground sloths. While some scientists attribute this extinction to human hunting, a closer examination of the evidence suggests that climate change was the primary driver. First, the timing of the extinctions correlates strongly with major climatic shifts. In North America, most megafauna vanished during the Younger Dryas, a sudden return to glacial conditions, not during periods of stable climate when humans were present. Second, many megafauna species were highly specialized, with large body sizes and low reproductive rates, making them especially vulnerable to rapid environmental changes that altered their habitats and food sources. For example, the woolly mammoth depended on vast steppe grasslands, which were replaced by forests and tundra as temperatures warmed. Third, human populations at the time were too small and their hunting technologies too primitive to cause such widespread extinctions across continents. Archaeological sites show that early humans primarily hunted small game and gathered plants, and only rarely did they target large animals. Therefore, the pattern of megafaunal decline aligns more closely with climatic upheaval than with 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。
The professor argues that the reading's claim about climate change as the main cause of megafauna extinctions is flawed. First, while the Younger Dryas was a cold period, many megafauna had survived previous glacial-interglacial cycles, such as the Eemian interglacial, which were equally drastic. Thus, climate alone cannot explain why they went extinct only when humans were present. Second, the reading underestimates the adaptability of megafauna. Fossil evidence shows that woolly mammoths shifted their diets and migrated to new areas when grasslands changed, indicating they were not as specialized as assumed. In contrast, human hunting pressure was intense and selective. Recent studies of kill sites reveal that early humans used sophisticated tactics, such as driving herds off cliffs, and could decimate entire populations in a short time. Third, the claim that human populations were too small is misleading. Even low-density populations, if they focus on megafauna, can cause extinction through 'blitzkrieg' hunting, as seen in New Zealand, where moa birds went extinct within a few centuries of Maori arrival. Moreover, the rapid climate shifts actually reduced human populations, yet extinctions continued, suggesting that hunting, not climate, was the constant factor.
📝 ライティング指示 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
📊 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).
