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, archaeological sites show that human populations in Siberia and North America were too sparse to have hunted mammoths to extinction. Even if each group killed several mammoths per year, the total number would not have significantly impacted a population that spanned millions of square kilometers. Second, the timing of mammoth extinction correlates more closely with rapid climate warming at the end of the Pleistocene than with human arrival. Mammoths survived on isolated islands like Wrangel Island for thousands of years after humans reached the mainland, which contradicts the idea that humans caused their demise everywhere. Third, mammoths were highly specialized to cold, dry steppe environments. As the climate warmed, forests and wetlands expanded, fragmenting their habitat and reducing their food supply. Isotopic analyses of mammoth bones reveal a shift toward less nutritious plants just before their final disappearance, indicating that environmental stress, not human hunting, was the critical factor.
🎧 听力讲座
The reading's argument that climate change alone explains mammoth extinction is unconvincing. First, while human populations were small, they were highly efficient hunters. Evidence from kill sites shows that they used sophisticated tactics, such as driving herds off cliffs, which could kill dozens at once. Even low-density human groups could have had a disproportionate impact on mammoths, which had slow reproductive rates. Second, the survival of mammoths on Wrangel Island actually supports the human overhunting theory. Mainland mammoths disappeared soon after humans arrived, but the island was not colonized by humans until much later. When humans finally reached Wrangel Island, the last mammoths vanished within a few centuries—a pattern consistent with hunting pressure. Third, the dietary shift mentioned in the reading is not proof of climate stress. It may reflect the fact that as mammoth populations declined due to hunting, survivors were forced into marginal habitats with poorer forage. In other words, the poor diet was a consequence of reduced population, not a cause of extinction. Thus, the evidence points to humans as the decisive factor, with climate playing only a secondary role.
📝 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.