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 (approximately 10,000 years ago), which drastically altered their grassland habitats. As temperatures rose, forests and tundra expanded, fragmenting the open steppe that mammoths depended on for food. Second, genetic studies reveal that mammoth populations experienced a severe bottleneck before human populations in the same regions became dense. For example, DNA from Siberian remains shows a steep decline in genetic diversity starting around 15,000 years ago, when human hunting pressure was still minimal. Third, the final refuge of mammoths on remote islands like Wrangel Island persisted for thousands of years after human arrival on the mainland, but they vanished soon after a period of extreme climate fluctuation, not after intensive hunting. These points indicate that environmental factors, not human activity, were the decisive cause.

🎧 リスニング講義

The reading's argument that climate change alone drove mammoth extinction is flawed. First, while warming did alter habitats, humans actively accelerated this process through landscape burning and the introduction of new predator-prey dynamics. Paleontological evidence shows that mammoth populations declined sharply in regions where humans arrived, even when similar climate shifts occurred in unpopulated areas. Second, the genetic bottleneck cited in the reading is misleading: the decline in diversity began earlier, but it was the sudden rise in human hunting, documented by butchered mammoth bones and spear points, that delivered the final blow. In fact, human population density in Siberia around 12,000 years ago was much higher than the reading assumes, and archaeological sites show mass kill events. Third, the Wrangel Island case actually supports the human theory. When humans finally reached Wrangel around 1700 BCE, the last mammoths disappeared within a few centuries, coinciding with a known hunting camp. Climate records for that period show no unusual change. Thus, human overhunting, not climate, was the primary cause.