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 hunting, but recent evidence suggests that climate change was the primary driver. First, the mammoth population began declining around 15,000 years ago, well before humans arrived in their main habitats in North America and Eurasia. This timing indicates that hunting could not have initiated the decline. Second, genetic studies of ancient mammoth remains reveal a severe loss of genetic diversity starting 20,000 years ago, which is consistent with a shrinking population due to habitat loss, not overhunting. Finally, the last known mammoths survived on remote Arctic islands, such as Wrangel Island, where human presence was minimal or absent until after their extinction. This suggests that environmental factors, such as the post-glacial warming and the resulting shift from grasslands to forests, were more critical than human activity.

🎧 リスニング講義

The reading's argument that climate change alone caused mammoth extinction is flawed. First, the claim about timing is misleading. While humans may not have been in North America 15,000 years ago, they were present in Eurasia earlier, and mammoth populations in Eurasia declined sharply exactly when human hunting expanded. Moreover, in areas like Siberia, human artifacts and mammoth bones are found together, indicating active hunting. Second, the genetic bottleneck cited in the reading can be explained by human hunting, which can also reduce population size and genetic diversity. In fact, many species that were hunted to near-extinction show similar genetic patterns. Third, the Wrangel Island example does not prove climate was the cause. The mammoths there survived until around 4,000 years ago, long after the climate stabilized, and their extinction coincides with the arrival of humans on the island. Thus, human hunting, not climate, best explains the final disappearance.