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 (about 10,000 years ago), when global temperatures rose dramatically. This warming caused a shift from dry, grassy steppes to wetter, forested landscapes, reducing the open grassland habitat that mammoths depended on for food. Second, paleontological studies show that mammoth populations began to shrink in isolated regions, such as islands off Siberia, long before humans arrived on those islands. For example, Wrangel Island mammoths survived until 4,000 years ago, but their numbers were already genetically declining due to inbreeding and reduced fertility, a sign of environmental stress rather than hunting pressure. Third, the rise of human hunters does not correlate with local extinction events in many areas. In parts of North America, mammoth fossils disappear thousands of years before the appearance of Clovis hunting tools, suggesting that other factors, such as vegetation changes, were more decisive. Therefore, while humans may have delivered the final blow in some regions, the overarching cause of mammoth extinction was a climate-induced habitat loss.

🎧 リスニング講義

The reading's argument that climate change alone drove mammoth extinction is unconvincing. First, while warming did alter habitats, mammoths were adaptable grazers that could survive in varied environments, as evidenced by their presence in both steppe and tundra regions. Moreover, the replacement of grasslands by forests was not instantaneous; it occurred over millennia, giving mammoths ample time to migrate or adjust. Second, the claim about Wrangel Island is misleading. Genetic studies show that the small population there was indeed inbred, but this was a result of isolation after sea levels rose, not a pre-existing decline. In fact, mammoths thrived on the island for over 6,000 years after the mainland extinction, which indicates that they could survive climate shifts if not hunted. Third, the correlation between human arrival and extinction is stronger than the reading admits. Recent archaeological finds in Alaska reveal mammoth bones with cut marks dating to 14,000 years ago, and genetic data show a rapid population crash that coincides with human expansion across the Bering Land Bridge. The lack of tools at some sites may simply reflect poor preservation or the use of organic weapons that decayed. Thus, human hunting, not climate, was the decisive factor in the final extinction.