托福综合写作

📖 阅读文章

The extinction of the woolly mammoth has long been attributed to human overhunting, but recent evidence suggests that climate change was the primary driver. First, the timing of mammoth decline coincides with the end of the last Ice Age, when global temperatures rose rapidly. As the glaciers retreated, the mammoth's preferred habitat—cold, dry steppe—shrunk dramatically, replaced by forests and wetlands. This habitat loss would have reduced food availability and increased competition with other herbivores. Second, genetic studies of mammoth remains show a severe population bottleneck around 20,000 years ago, well before humans arrived in large numbers in Siberia and North America. This indicates that climate-induced stress had already weakened the species. Third, archaeological evidence reveals that human hunting was sporadic and localized. Clovis spear points, for example, are rare at mammoth kill sites, and many human settlements date after the major mammoth decline. Thus, while humans may have delivered the final blow, climate change was the fundamental cause.

🎧 听力讲座

The lecture challenges the reading's conclusion that climate change was the primary cause of mammoth extinction. While the reading cites habitat loss, the lecturer argues that mammoths were highly adaptable. Fossil pollen and plant remains show that mammoths shifted their diet to include grasses and sedges in newly formed wetlands, so vegetation changes alone cannot explain their demise. Moreover, the genetic bottleneck mentioned in the reading actually occurred 20,000 years ago, but mammoth populations rebounded afterward, thriving for another 10,000 years. This recovery suggests that climate fluctuations were not always fatal. Most importantly, the lecture points to recent archaeological finds in Alaska and Siberia that reveal numerous butchered mammoth bones with clear cut marks, dated to the period of final extinction. These sites are far more common than previously thought, indicating that human hunting pressure was intense and widespread. In addition, the timing of the final extinction varies by region—some isolated islands retained mammoths until 4,000 years ago, long after the climate stabilized. Therefore, the lecture concludes that human overhunting, not climate, was the decisive factor.