TOEFL統合ライティング

📖 読解文章

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 significantly. As the ice retreated, the open grasslands that mammoths depended on were replaced by dense forests and wetlands, which were unsuitable for their grazing lifestyle. Second, genetic studies of ancient mammoth remains reveal a dramatic loss of genetic diversity just before extinction, indicating a population bottleneck caused by habitat fragmentation rather than sudden hunting pressure. Finally, human populations at the time were small and sparsely distributed, with limited hunting technology, making it unlikely they could have killed enough mammoths to cause extinction, especially given that mammoths had survived alongside humans for thousands of years before their final disappearance.

🎧 リスニング講義

The lecture challenges the reading's claim that climate change alone caused the woolly mammoth's extinction. While the timing of the end of the Ice Age is correct, the reading overlooks that similar climate shifts had occurred many times before without leading to extinction. In fact, mammoths thrived during previous interglacial periods, so they were adaptable to warmer conditions. The genetic bottleneck mentioned in the reading actually supports human hunting: a sudden reduction in population, as seen in the genetic record, is more consistent with rapid overkill than with gradual habitat loss, which would cause a slow decline over many generations. Moreover, the reading underestimates human capabilities. Archaeological sites show sophisticated hunting tools, such as spears with sharp stone points and perhaps even traps, and human populations were larger than previously thought. Evidence from islands where mammoths survived longer, such as Wrangel Island, indicates that these populations only disappeared after humans arrived, despite having survived earlier climate changes. Thus, the lecture argues that human hunting, not climate, was the decisive factor.