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 timing of mammoth decline coincides with the end of the last Ice Age, when temperatures rose dramatically. As the glaciers retreated, the open grasslands that mammoths depended on were replaced by dense forests and wetlands, reducing their grazing habitat. Second, genetic studies of fossil remains show a sharp decline in genetic diversity among mammoths around 20,000 years ago, well before human populations reached peak hunting pressure in North America and Eurasia. This bottleneck suggests that environmental stress, not hunting, caused population fragmentation. Third, archaeological sites from the period contain relatively few mammoth bones with clear cut marks, indicating that humans did not rely on them as a primary food source. Instead, early humans likely scavenged already dead animals, as mammoth carcasses would have been abundant during natural die-offs. Therefore, climate-driven habitat loss, not human predation, led to their demise.
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The reading's argument that climate change alone drove mammoth extinction is flawed. While it is true that habitats shifted, this does not exclude human impact. In fact, human hunting may have delivered the final blow to populations already stressed by climate. For example, the reading cites a genetic bottleneck 20,000 years ago, but this predates the final extinction by thousands of years. If climate were the sole cause, mammoths should have died out then, yet they survived until about 4,000 years ago on isolated islands. This survival indicates that they could adapt to some environmental changes. Moreover, the scarcity of cut marks on mammoth bones is misleading. Early humans likely used spears and drove mammoths into bogs or traps, where they drowned or were killed without leaving butchering marks. In such cases, the bones might not show evidence of hunting. Finally, the reading overlooks the fact that human populations expanded dramatically exactly when mammoth numbers crashed. In Siberia and Alaska, the arrival of the Clovis people correlates with a rapid decline in mammoth populations, a pattern consistent with overhunting. Thus, climate stress may have weakened mammoths, but human predation was the decisive factor.
📝 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.
