The extinction of the woolly mammoth has long been attributed to human hunting, but a closer examination of the evidence suggests that climate change was the primary driver. First, the timing of mammoth extinctions correlates more strongly with climatic shifts than with human arrival. In North America, mammoths disappeared around 10,000 years ago, during the rapid warming at the end of the last ice age, while humans had been present for at least 2,000 years before that. If hunting were the main cause, we would expect extinction to follow soon after human arrival, not millennia later. Second, mammoth populations showed signs of stress before human contact. Genetic studies of mammoth remains from Siberia reveal a decline in genetic diversity starting about 20,000 years ago, well before humans reached that region. This indicates that shrinking populations were already vulnerable due to environmental changes, not due to overhunting. Third, the habitat that mammoths depended on—cold, dry grasslands known as steppe-tundra—dramatically shrank as the climate warmed and became wetter, leading to the spread of forests and bogs. This loss of preferred vegetation would have reduced food availability and fragmented populations, making survival increasingly difficult. While human hunting may have delivered a final blow to isolated groups, the overwhelming evidence points to climate change as the decisive factor in the mammoth's demise.
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The reading's argument that climate change alone drove the woolly mammoth to extinction is unconvincing. While it's true that climatic shifts occurred, the correlation with extinction timing is weak. In many regions, mammoths survived periods of warming that were just as severe as the one at the end of the ice age. For instance, mammoths persisted in Siberia through interglacial warm spells long before humans arrived. Their extinction only occurred after humans with advanced hunting tools appeared, suggesting that human predation was the critical new factor. Second, the genetic diversity decline cited in the reading is not evidence of climate stress. Similar declines are seen in other large mammals that were hunted by humans, such as the giant ground sloth. Such declines can result from selective hunting of the largest individuals, which reduces population size and genetic variation over time—not from environmental changes. Finally, while steppe-tundra did shrink, mammoths were not strictly dependent on that habitat. Fossil evidence shows they also thrived in mosaic environments, including shrublands and even some forest edges. The real reason they disappeared is that humans, who were efficient hunters, followed them into these new habitats and systematically killed them off. Therefore, the reading's claim that climate change was primary is misguided; human hunting 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.
