The extinction of the woolly mammoth has long been attributed to human hunting, but recent evidence suggests that climate change was the primary driver. First, the timing of mammoth decline correlates with the end of the last Ice Age, when temperatures rose rapidly. As the glaciers retreated, the open grasslands that mammoths depended on were replaced by dense forests and tundra, reducing their food supply. Second, genetic studies of fossil remains show that mammoth populations experienced severe bottlenecks long before humans arrived in their habitats. For example, DNA from mammoths on Wrangel Island indicates a drastic population drop around 20,000 years ago, predating human presence by several millennia. Third, the hunting hypothesis fails to explain why other large herbivores, such as the steppe bison, also went extinct at the same time. If human hunters were the cause, they would have targeted easier prey, but bison were equally affected, pointing to a shared environmental cause. Thus, climate-driven habitat loss, not overhunting, led to the mammoth's demise.
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The reading's claim that climate change alone caused mammoth extinction is oversimplified. While temperature shifts did alter habitats, human hunting played a decisive role. First, the correlation between warming and mammoth decline is not straightforward. Mammoths survived previous interglacial warm periods, such as the Eemian, without going extinct. What was different this time was the arrival of skilled human hunters, who used advanced weapons and drove herds off cliffs. Second, the genetic bottlenecks cited in the reading actually support the hunting hypothesis. The population drop on Wrangel Island occurred not 20,000 years ago but around 4,000 years ago, when humans are known to have reached the island with boats. The earlier DNA dates in the reading have been re-evaluated and found to be contaminated. Third, the extinction of steppe bison is not analogous because bison populations rebounded in North America, while mammoths did not. This suggests that bison adapted to new environments, whereas mammoths were specifically hunted to extinction by humans who valued their tusks and meat. Therefore, hunting, not climate, was the primary cause.
📝 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.
