The extinction of the woolly mammoth, a massive herbivore that roamed the Arctic tundra until roughly 4,000 years ago, has long puzzled scientists. While many blame human hunting, a closer look at the evidence suggests that climate change was the primary driver. First, the timing of the mammoth’s final decline coincides with the Holocene warming period, when temperatures rose dramatically and vegetation shifted from nutritious grasses to less digestible shrubs and mosses. This dietary stress would have reduced fertility and increased mortality, especially among calves. Second, genetic studies of late-surviving mammoth populations reveal low genetic diversity, indicating small, isolated groups that were vulnerable to inbreeding and disease—conditions exacerbated by shrinking habitats. Finally, human hunting pressure was likely minimal in the Arctic, where human populations were sparse and relied more on fishing and marine mammals than on terrestrial game. Archaeological sites from the period show few mammoth kills, and the species survived for millennia alongside humans in Siberia and Alaska, suggesting that hunting was not the decisive factor.
🎧 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。
The lecture challenges the reading’s claim that climate change alone caused the woolly mammoth’s extinction. First, while the Holocene warming did reduce grasslands, similar warming events occurred earlier in the mammoth’s history without causing extinction. For example, the Eemian interglacial, which was even warmer than the Holocene, saw mammoths thrive. Thus, vegetation shifts alone cannot explain their demise. Second, low genetic diversity in late populations is not necessarily a natural consequence of climate; rather, it reflects the fragmentation caused by human encroachment and hunting, which pushed mammoths into isolated refuges. In fact, genetic bottlenecks often result from overhunting, not gradual environmental change. Third, the reading underestimates human impact. Recent archaeological finds in Siberia include spear points with mammoth DNA and butchery marks on bones, indicating active hunting. Moreover, human populations were growing and expanding precisely as mammoth numbers crashed, and the arrival of advanced hunting technologies, such as the Clovis spear, coincided with rapid declines in North America. Therefore, human hunting, not climate, was the decisive factor.
📝 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.
