The extinction of the woolly mammoth, a species that roamed the Arctic tundra until roughly 4,000 years ago, has long been attributed to human overhunting. However, a closer examination of the evidence suggests that climate change was the primary driver, not human activity. First, paleoclimatic data show that the last glacial period ended around 10,000 years ago, leading to a dramatic warming trend. This warming caused the spread of boreal forests and wetlands, which replaced the open grassland steppe that mammoths depended on for food. As their primary habitat shrank, mammoth populations likely fragmented and declined. Second, archaeological evidence from sites like the Wrangel Island, where mammoths survived until 4,000 years ago, reveals no clear signs of human hunting—no spear points or butchering marks on mammoth bones. If humans were the main cause, we would expect to find such artifacts at the last refuges. Third, genetic studies of ancient mammoth remains show a significant loss of genetic diversity in the final millennia, indicating that populations became small and isolated. This genetic bottleneck is more consistent with a gradual habitat-driven decline than with a sudden, selective kill-off by hunters.
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The reading’s argument that climate change alone drove woolly mammoth extinction is unconvincing. While it is true that habitats shifted, the mammoths were not passive victims of vegetation change. In fact, mammoths themselves helped maintain the grassland steppe by trampling trees and fertilizing the soil with their dung. When human hunters appeared, they reduced mammoth numbers, and once this ‘ecosystem engineering’ stopped, the grasslands transformed into forests, accelerating the decline. Thus, climate only became a factor after human hunting tipped the balance. Second, the absence of human artifacts on Wrangel Island is not evidence against hunting. The island’s small mammoth population could have been wiped out by a small group of hunters within just a few centuries, and the archaeological record may simply be incomplete due to coastal erosion and rising sea levels that submerged many former sites. Other regions, such as the Yukon, show clear mammoth spear points and butchering sites dating to the arrival of humans. Finally, the genetic bottleneck cited in the reading actually supports the human-hunting hypothesis: a rapid population crash caused by overhunting would also leave a genetic signature of reduced diversity, and the timing of the bottleneck on Wrangel Island (around 4,000 years ago) coincides with the first human arrival on the island, not with any major climate shift.
📝 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.
