TOEFL統合ライティング

📖 読解文章

The extinction of the megafauna—large animals such as mammoths, giant sloths, and saber-toothed cats—at the end of the Pleistocene epoch has long puzzled scientists. While many theories exist, the most compelling explanation is overhunting by early humans. First, archaeological evidence shows that human arrival in new regions closely correlates with rapid megafaunal decline. For instance, in North America, the Clovis culture appeared around 13,000 years ago, and within a few centuries, most large mammals vanished. Second, the selective extinction of large-bodied species supports the hunting hypothesis. These animals had slow reproductive rates and would have been especially vulnerable to human predation, whereas smaller species, which were less targeted, survived. Third, kill sites with butchered remains, such as the Lehner site in Arizona, provide direct proof that humans hunted these animals. Although some argue that climate change was responsible, the fact that previous interglacial warm periods did not cause such extinctions suggests that human activity, not climate, was the decisive factor.

🎧 リスニング講義

The professor challenges the reading's claim that human overhunting caused megafaunal extinction. While the correlation between human arrival and extinction is suggestive, it is not causal. For example, in Africa and Asia, where humans evolved and coexisted with megafauna for hundreds of thousands of years, many large animals survived until recently. If humans were such efficient hunters, these species should have disappeared much earlier. Second, the selective extinction of large animals can be better explained by climate change. Large-bodied animals have higher metabolic demands and require more food and water. During the dramatic climate shifts at the end of the Pleistocene, their habitats shrank, and their food sources became scarce. Small animals, with lower resource needs, could adapt more easily. Third, the so-called kill sites are rare and often ambiguous. Many sites contain bones that show signs of scavenging, not hunting. For instance, at the Lehner site, bones may have been broken by natural processes or carnivores, not by human tools. Moreover, if humans were the primary cause, we would expect far more kill sites given the number of extinctions. The evidence better supports a climate-driven extinction, as the most severe losses occurred during periods of rapid temperature and vegetation change.