The extinction of the woolly mammoth has long been attributed to overhunting by early humans, but recent evidence suggests that climate change was the primary driver. First, the timing of mammoth extinctions correlates more closely with rapid warming periods than with human arrival in most regions. For example, in North America, mammoths disappeared around 10,000 years ago, which coincides with the end of the last Ice Age, while humans had already been present for at least 2,000 years. Second, the warming climate reduced the mammoth’s preferred habitat—cold, dry grasslands—by converting them into forests and wetlands, which are unsuitable for large grazing herbivores. Fossil pollen records from Siberia and Alaska show a sharp decline in grass species just before mammoth numbers plummeted. Third, mammoths had low genetic diversity in their final populations, as revealed by ancient DNA studies. This suggests that they were already struggling to adapt to environmental stress, making them vulnerable to extinction even without human hunting. Therefore, while humans may have contributed locally, the overarching cause was climate-induced habitat loss and the inability of mammoths to cope with rapid ecological shifts.
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The reading’s claim that climate change alone drove the woolly mammoth to extinction is not supported by the evidence. First, the correlation between warming and extinction is misleading. In many areas, mammoths survived later warming events, such as the interglacial periods before the last Ice Age, but they vanished only after humans arrived. For instance, on Wrangel Island, mammoths persisted until about 4,000 years ago, well after the climate had stabilized, but they disappeared shortly after human colonization. Second, although grasslands did decline, mammoths were not strictly dependent on that habitat. Isotopic analysis of mammoth bones shows they could consume a variety of vegetation, including shrubs and herbs, which remained available. Moreover, other large herbivores like caribou thrived in the same changing environments, indicating that the habitat was not universally hostile. Third, the low genetic diversity cited in the reading is a consequence, not a cause, of small population sizes. Such bottlenecks can occur naturally, but they do not necessarily lead to extinction; many species with low diversity have survived for millennia. The final blow on Wrangel Island was likely human hunting, as archaeological evidence shows butchered mammoth remains. Thus, while climate may have weakened mammoth populations, it was human overhunting that delivered the fatal blow.
📝 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.
