TOEFL統合ライティング

📖 読解文章

The extinction of the woolly mammoth has long been attributed to overhunting by early humans, but recent evidence suggests that climate change was the primary driver. First, the timing of the mammoth’s decline coincides with the end of the last Ice Age, when global temperatures rose dramatically. As the ice retreated, the vast grasslands known as the mammoth steppe shrank, reducing the available habitat and food supply. Second, genetic studies of mammoth remains show a significant loss of genetic diversity before their final extinction, indicating population stress from environmental fragmentation rather than sudden human predation. Finally, archaeological sites with mammoth bones and human tools are rare, and many of these bones show no signs of butchering. In contrast, other megafauna that were clearly hunted, such as the giant bison, show abundant kill sites. Therefore, the woolly mammoth’s disappearance was likely a consequence of natural habitat loss, not human hunting.

🎧 リスニング講義

The professor challenges the reading’s claim that climate change alone caused the woolly mammoth’s extinction. While it is true that the mammoth steppe shrank, the professor points out that similar warm periods occurred earlier in the mammoth’s history without causing extinction. For example, during the Eemian interglacial, about 125,000 years ago, temperatures were even warmer and the steppe contracted, yet mammoths survived. Second, the genetic diversity loss mentioned in the reading can be explained by human hunting, which reduces population size rapidly and leads to inbreeding and genetic bottlenecks. The professor cites models showing that even low levels of hunting by a small human population could cause the observed genetic decline. Finally, the scarcity of kill sites is not surprising because early humans likely scavenged or used only parts of the mammoth, leaving little evidence. In addition, rising sea levels after the Ice Age may have submerged many coastal kill sites. Thus, the professor concludes that human activity, not climate, was the decisive factor.