The extinction of the woolly mammoth has long been attributed to human overhunting, but recent evidence suggests that climate change was the primary driver. First, the timing of mammoth extinctions correlates more closely with climatic shifts than with human arrival. In North America, mammoths disappeared around 10,000 years ago, during a period of rapid warming and vegetation change, whereas humans had been present for at least 2,000 years before that. Second, mammoth populations showed signs of decline before significant human hunting pressure existed. Genetic studies of ancient DNA reveal a steady loss of genetic diversity starting about 20,000 years ago, well before human populations expanded in the Arctic. Third, the habitat that mammoths depended on—the mammoth steppe—shrank dramatically as warming climates allowed forests and wetlands to replace grasslands. This habitat loss would have reduced available food and increased competition with other herbivores, leading to population crashes even in the absence of hunting. Therefore, while humans may have delivered the final blow, climate-driven habitat change was the decisive factor in the mammoth's demise.
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The reading's claim that climate change alone drove mammoth extinction is not convincing. While it is true that climate warmed and habitats changed, similar climatic shifts had occurred many times before, yet mammoths survived those earlier changes. The crucial difference at the end of the Pleistocene was the presence of highly skilled human hunters. First, the correlation between human arrival and extinction is stronger than the reading suggests. In Eurasia, mammoths persisted until humans arrived in their final refuges, such as Wrangel Island, where they survived for thousands of years after the climate had warmed—only to disappear shortly after human colonizers reached the island. Second, the genetic diversity decline cited in the reading can be explained by human hunting, which would have reduced population sizes and thus genetic variation, rather than by climate-induced bottlenecks. Third, the habitat change argument overlooks the fact that mammoths were adaptable; they could have migrated to other grassland areas or altered their diet. In fact, fossil evidence shows that some mammoth populations survived in boreal forests by eating shrubs and tree bark. The real killer was likely the combination of habitat fragmentation and relentless human predation, with hunting preventing populations from recovering from any environmental stress.
📝 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.
