TOEFL統合ライティング

📖 読解文章

The Extinction of the Megafauna: A Climate-Driven Event During the Pleistocene epoch, large terrestrial mammals—such as woolly mammoths, giant ground sloths, and saber-toothed cats—disappeared from North America and Eurasia. While some scientists attribute this extinction to human hunting, a closer examination of the evidence suggests that climate change was the primary driver. First, the timing of the extinctions correlates with the last glacial retreat, which caused dramatic shifts in vegetation and habitat. As temperatures warmed, the open grasslands and tundra that supported these megafauna shrank, reducing their food sources and leading to population collapses. Second, many megafauna species had successfully coexisted with humans for millennia before their final disappearance. For example, archaeological sites show that early humans hunted these animals, but the hunting pressure was likely too low to cause extinction, especially given the low human population densities at the time. Third, the fossil record reveals that megafauna populations were already in decline before the arrival of humans in many regions. In Australia, for instance, extinctions occurred around 45,000 years ago, but human arrival is dated to 50,000 years ago, leaving a short overlap that does not support a hunting-driven extinction. Instead, the pattern aligns with climate-induced environmental stress.

🎧 リスニング講義

Now listen to a lecture on the same topic. Professor: The reading claims that climate change, not human hunting, drove the megafauna extinctions. However, that view is seriously flawed. First, while the timing of the extinctions does overlap with the last glacial retreat, this correlation is not causal. In fact, many regions experienced similar climatic shifts during earlier interglacial periods, yet megafauna did not go extinct then. For example, during the previous interglacial, the climate was just as warm, and yet woolly mammoths survived. So climate change alone cannot explain why they died out only when humans were present. Second, the argument that humans coexisted with megafauna for millennia without causing extinction ignores the fact that hunting pressure can be intense even at low population densities. Modern hunter-gatherers have been shown to drive prey to extinction through selective hunting of juveniles and pregnant females, and the archaeological record shows that early humans used sophisticated tactics like driving herds off cliffs. Over thousands of years, such practices could easily have pushed vulnerable species over the edge. Third, the claim that Australian extinctions predate human arrival is based on unreliable dating. More recent radiocarbon and optically stimulated luminescence dating have revised the timing of human arrival in Australia to 65,000 years ago, which is well before the extinctions. Moreover, the fossil record shows a clear chronological pattern: as humans spread across the continent, megafauna disappeared, which strongly implicates hunting as the primary cause.