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 rapid warming at the end of the last Ice Age, around 10,000 years ago. As temperatures rose, their cold-adapted grassland habitat (the “mammoth steppe”) shrank dramatically, fragmenting populations and reducing food availability. Second, genetic studies of ancient mammoth remains show a significant loss of genetic diversity and a rise in harmful mutations just before extinction, indicating small, isolated populations that struggled to survive—a signature of environmental stress rather than sudden human hunting pressure. Third, human populations in regions like Siberia and North America were sparse at the time, with archaeological evidence showing only occasional hunting, not the widespread slaughter needed to drive such a large species to extinction. In contrast, the warming climate directly altered vegetation, water sources, and seasonal cycles, creating conditions that were inhospitable for mammoths across their entire range. Therefore, while humans may have delivered a final blow to remnant populations, the primary cause of woolly mammoth extinction was climate-driven habitat loss.

🎧 リスニング講義

The reading’s argument that climate change drove woolly mammoth extinction is flawed. First, while warming did occur, similar warming events had happened earlier in the mammoth’s history without causing extinction. For example, during interglacial periods before, mammoths survived and even thrived in warmer conditions by shifting their ranges. The real change 10,000 years ago was the arrival of highly skilled human hunters with advanced weapons. Second, the genetic evidence cited in the reading—low diversity and harmful mutations—actually points to a rapid population crash, which is more consistent with overhunting than a gradual habitat loss. Climate-driven habitat fragmentation would have caused a slow decline over millennia, but the genetic data show a sudden bottleneck, aligning with the swift spread of humans into new territories. Third, the claim that human populations were too sparse is misleading. Even small numbers of hunters can cause extinction of naive, slow-reproducing megafauna, especially when they target juveniles and females. Archaeological sites in Siberia and Alaska contain mammoth bones with cut marks, and the pattern of extinction closely follows the path of human migration. In sum, the lecture argues that the reading ignores the key role of human hunting, which acted as a catastrophic additional pressure on mammoth populations already stressed by environmental change.