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 mammoth population began to decline long before humans arrived in its habitats. Fossil records from Siberia and North America show a steady decrease in mammoth numbers starting around 20,000 years ago, while human migration into these regions occurred only about 15,000 years ago. This temporal gap implies that climate, not hunting, initiated the decline. Second, the mammoth’s habitat, the mammoth steppe, was highly sensitive to warming. As the Ice Age ended, rising temperatures and increased precipitation converted the dry, grassy steppe into wet, forested tundra, reducing the open grazing land that mammoths required. This vegetation shift would have diminished food availability, leading to malnutrition and lower reproductive rates. Third, climate models indicate that the final extinction events on Wrangel Island and St. Paul Island coincided with abrupt climate anomalies, such as droughts or sea-level rise, rather than with human presence. On St. Paul Island, radiocarbon dating shows that mammoths died out around 5,600 years ago, shortly after a period of severe drought that shrank the island’s freshwater sources—a scenario unrelated to hunting, as no human artifacts have been found there.
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The lecture challenges the reading’s claim that climate change alone drove mammoth extinction. While it is true that mammoth numbers declined before humans arrived, this does not rule out hunting. In fact, early human populations may have existed in these regions earlier than the fossil record suggests, as archaeological evidence is often incomplete due to rising sea levels and erosion. Moreover, the reading overlooks that the vegetation shift, while reducing grassland, did not eliminate all edible plants. Mammoths were generalist feeders and could adapt to shrubs and trees; indeed, studies of mammoth dung show they consumed a variety of plants even during the late Pleistocene. More critically, the lecture points out that climate change was not uniform across all mammoth habitats. On Wrangel Island, for instance, the climate remained stable for thousands of years after humans arrived elsewhere, yet mammoths still vanished around 4,000 years ago. This suggests that other factors, such as hunting by newly arrived humans, were decisive. Finally, regarding St. Paul Island, the lecture notes that the drought occurred 300 years before the mammoth extinction, and the mammoths actually recovered after the drought ended. Their final disappearance aligns with the arrival of human hunters on the island, as evidenced by stone tools and fire pits dated to that time. Thus, the lecture argues that overhunting, not climate, was the ultimate 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.
