The extinction of the woolly mammoth has long been attributed to human overhunting, a theory known as the Pleistocene overkill hypothesis. However, recent evidence suggests that climate change, not human activity, was the primary driver of their demise. First, the warming climate at the end of the last Ice Age drastically reduced the mammoth's preferred habitat—cold, dry grasslands known as the mammoth steppe. As temperatures rose, these grasslands were replaced by forests and wetlands, which were unsuitable for mammoths. Second, the climate change also altered migration patterns and reduced food availability, leading to nutritional stress. Fossil records show that late-surviving mammoth populations had smaller body sizes and tooth abnormalities consistent with malnutrition. Third, if humans were the main cause, we would expect a rapid extinction following human arrival. However, mammoth populations on remote islands, such as Wrangel Island, survived for thousands of years after humans reached the mainland, and even coexisted with humans for millennia in some regions. This delayed extinction pattern aligns more closely with gradual climate shifts than with sudden human hunting pressure.
🎧 听力讲座
The reading's argument that climate change alone caused mammoth extinction is flawed. While climate change did alter habitats, it was not the decisive factor. First, mammoths were highly adaptable and had survived previous warm interglacial periods without going extinct. For example, they thrived during the Eemian interglacial, which was warmer than the present, indicating that warming alone does not explain their disappearance. Second, the nutritional stress observed in late mammoths can be directly linked to human hunting, not climate. Hunters preferentially targeted healthy adults, disrupting social structures and reducing the population's ability to reproduce and maintain genetic diversity. The resulting inbreeding and reduced fitness would manifest as the skeletal abnormalities the reading cites. Third, the survival of mammoths on Wrangel Island actually supports the overkill hypothesis. The island was isolated and human hunters arrived late, so mammoths survived until humans finally reached it. Similarly, mainland mammoths went extinct shortly after humans arrived, but on the island, extinction occurred within a few hundred years of human colonization. This pattern—extinction following human arrival—is a classic signature of hunting pressure, not climate.
📝 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.