The extinction of the woolly mammoth has long been attributed to overhunting by early humans. However, recent evidence suggests that climate change was the primary driver. First, the warming period at the end of the Pleistocene reduced the mammoth's grassland habitat. As forests and tundra expanded, the open steppe ecosystems that mammoths depended on shrank dramatically, leading to population fragmentation and decline. Second, climate models show that rapid temperature increases caused shifts in plant communities, reducing the nutritional quality of available forage. Isotopic analysis of mammoth bones from this period reveals a diet increasingly composed of woody plants, which are less digestible and lower in protein, compromising their health and reproductive success. Third, the timing of human arrival in different regions does not consistently correlate with mammoth extinction. In some areas, such as Wrangel Island, mammoths survived for thousands of years after human contact, while in others, like the Eurasian mainland, they vanished before significant human settlement. This pattern suggests that environmental factors, not human hunting, were the decisive influence. Therefore, while human activity may have contributed locally, the overarching cause of woolly mammoth extinction was climate-driven habitat loss and dietary stress.
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The reading's argument that climate change alone drove woolly mammoth extinction is flawed. First, while grasslands did shrink, mammoths were not strictly tied to open steppe. Fossil evidence shows they adapted to varied environments, including forested areas, and their dietary range was broader than assumed. The isotopic data cited actually reflect seasonal or regional variation, not a universal decline in nutrition. Second, the timing argument is misleading. Human hunting pressure need not be constant or widespread to cause extinction; even sporadic hunting of already stressed populations, especially juveniles, could push them over the edge. Moreover, archaeological sites with mammoth kill sites and tool marks are more numerous than the reading acknowledges, particularly in the Americas and Siberia, where extinctions closely followed human arrival. Third, the Wrangel Island survival is not a counterexample but a consequence of isolation and low human presence. The island's mammoths were dwarfs with reduced fertility, and they eventually disappeared around the time humans first arrived there, suggesting that even minimal contact was fatal. In sum, the reading underestimates the synergistic effect of climate stress and human predation, where hunting was the final blow to already vulnerable populations.
📝 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.
