The Extinction of the Megafauna: A Climate-Driven Event
During the late Pleistocene, approximately 50,000 to 10,000 years ago, many large terrestrial mammals—such as woolly mammoths, saber-toothed cats, and giant ground sloths—went extinct. While some scientists attribute these extinctions to human hunting, a closer examination of the evidence suggests that climate change was the primary driver. First, the timing of the extinctions correlates strongly with major climatic shifts, not with human arrival. In North America, the last glacial maximum occurred around 20,000 years ago, followed by a rapid warming period known as the Bølling-Allerød interstadial. Fossil records show that many megafauna species disappeared during these abrupt temperature changes, thousands of years before the widely accepted Clovis hunting culture appeared around 13,000 years ago. Second, climate change directly altered habitats. As temperatures rose, vast grasslands and steppe ecosystems—which supported grazing megafauna—were replaced by forests and tundra. This reduction in suitable forage would have stressed herbivore populations, and consequently, the carnivores that preyed on them. For example, the woolly mammoth relied on dry, cold steppe vegetation; when this habitat shrank, mammoth populations dwindled. Third, the extinction patterns were not uniform across all species, as would be expected if human hunters were the sole cause. Instead, species with specialized dietary needs and limited geographic ranges—such as the giant short-faced bear—suffered disproportionately, while more adaptable species survived. This selective extinction aligns with climate-induced habitat loss rather than overhunting, which would have targeted large, slow-reproducing animals regardless of their ecological niche.
🎧 听力讲座
🎯 模拟考试环境：先点「播放讲座」听完内容，再作答。听力原文默认隐藏。
Now listen to part of a lecture on the same topic.
Professor: The reading argues that climate change, not human hunting, drove the megafauna extinctions. However, this view is flawed. Let me explain. First, the timing argument is misleading. While some extinctions occurred during warming periods, many megafauna species coexisted with earlier human populations for thousands of years. For instance, in Australia, megafauna such as the giant kangaroo disappeared around 46,000 years ago, shortly after humans arrived, but there was no major climatic shift at that time. Similarly, in North America, the Clovis people appeared around 13,500 years ago, and within a few hundred years, most megafauna vanished—a pattern consistent with overhunting, not gradual climate change. Second, the habitat-loss claim is overstated. Many megafauna were generalists, not specialists. Fossilized dung and teeth show that woolly mammoths, for example, could eat a wide variety of plants, including grasses, sedges, and even woody shrubs. So they were not solely dependent on steppe vegetation. Moreover, climate-driven habitat shifts had occurred many times before without causing extinctions, which suggests that climate alone is insufficient. Third, the selective extinction pattern actually supports human hunting. Hunters preferentially targeted large, slow-reproducing animals—exactly the species that went extinct. Species with smaller body sizes and faster reproductive rates, like deer and rabbits, survived because they could replenish their numbers. This is a classic signature of human overexploitation, not climate. In sum, the evidence strongly implicates human activity as the primary cause.
📝 写作提示 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
