The extinction of the woolly mammoth has long been attributed to human overhunting. However, a more recent hypothesis suggests that climate change was the primary driver. This argument rests on three key observations. First, the woolly mammoth’s habitat, the mammoth steppe, expanded and contracted with glacial cycles. During the last glacial maximum, the steppe covered vast areas of Eurasia and North America, providing abundant grass. As the climate warmed and glaciers retreated, the steppe shrank, replaced by forests and wetlands, which were unsuitable for mammoths. Second, the timing of extinction closely correlates with the end of the last ice age, around 10,000 years ago, rather than with the arrival of humans in each region. For instance, mammoths survived on Wrangel Island until 4,000 years ago, long after humans had arrived, but only after the island’s vegetation had shifted to dwarf shrubs. Third, genetic evidence from ancient mammoth remains shows a decline in genetic diversity before extinction, indicating small, isolated populations that were vulnerable to environmental stress. This pattern is consistent with climate-driven habitat fragmentation, not with sudden overhunting by humans.
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The reading’s claim that climate change alone drove mammoth extinction is unconvincing. First, the correlation between habitat change and extinction is not as neat as presented. While the steppe did shrink, mammoths were not strictly grazers; analysis of their fossilized dung and tooth wear reveals they also browsed on shrubs and tree bark. Thus, forested environments could have supported them. Second, the survival on Wrangel Island actually undermines the climate argument. The island’s vegetation changed to dwarf shrubs, yet mammoths persisted for thousands of years. This shows they could adapt to altered flora. What finally killed them was likely human hunting—archaeological evidence shows humans on the island at the time of their disappearance. Third, the decline in genetic diversity is not a cause but a consequence of small population size. Small populations are more vulnerable to any threat, including hunting. In fact, the genetic data show a sudden drop in diversity around the time of human arrival in each region, not a gradual decline over millennia. This pattern points to rapid overkill, not slow environmental pressure. Therefore, the evidence better supports human hunting as 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.
