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 correlates more closely with the end of the last Ice Age (around 10,000 years ago) than with the arrival of human hunters. In North America, humans arrived at least 15,000 years ago, yet mammoths thrived for another 5,000 years, only disappearing as the climate warmed dramatically. Second, mammoth populations also collapsed in regions with sparse human presence, such as Arctic islands (e.g., Wrangel Island) where humans arrived late or not at all, yet the species vanished due to shrinking habitat and food scarcity. Finally, genetic studies of fossil remains show a severe loss of genetic diversity before extinction, indicating a population already stressed by environmental changes, not sudden overkill. These factors point to climate-induced habitat loss—shrinking grasslands and tundra—as the decisive cause.

🎧 リスニング講義

The reading's climate-only theory is flawed. First, the correlation with warming is misleading: humans reached Siberia and North America much earlier than 15,000 years ago, and their hunting pressure intensified over time. In fact, mammoth populations crashed precisely as human hunting technologies improved, such as the Clovis spear points, which appear in the fossil record at the same time as mass die-offs. Second, the Wrangel Island example actually supports human involvement. While humans arrived late there, the mammoths that survived on the island were dwarfs, and when humans finally arrived (around 4,000 years ago), the last mammoths disappeared within a few centuries—a classic pattern of overhunting. Third, the genetic diversity loss cited is not evidence of climate stress; it is a natural consequence of small population sizes, which could also result from hunting-induced population fragmentation. Furthermore, climate shifts at the end of the Ice Age were not uniform; some regions actually became more suitable for mammoths, yet they still vanished, which climate alone cannot explain. Thus, human hunting remains the more plausible primary cause.