The extinction of the woolly mammoth has long been attributed to human hunting, but recent evidence suggests that climate change was the primary driver. First, the mammoth's range contracted dramatically as the Earth warmed at the end of the Pleistocene. Fossil records show that mammoths once inhabited vast areas of Eurasia and North America, but as forests replaced grasslands, their habitat shrank to isolated pockets. This habitat loss would have reduced food availability and population sizes, making them vulnerable to extinction regardless of human activity. Second, the timing of mammoth extinction correlates more closely with climate shifts than with human arrival. In many regions, humans coexisted with mammoths for thousands of years before the animals disappeared, whereas the most rapid warming events coincided with their final extinction. Third, genetic studies of ancient mammoth remains reveal a decline in genetic diversity before their demise, a signature of small, stressed populations. Such genetic bottlenecks are more consistent with environmental pressures than with overhunting, which would not necessarily reduce genetic variation if populations remained large. Therefore, while humans may have played a minor role, the overwhelming evidence points to climate-induced habitat change as the main cause of the woolly mammoth's extinction.
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The reading's claim that climate change alone drove the woolly mammoth to extinction is not convincing. First, while it is true that mammoth habitats shrank, this does not exclude human hunting as a critical factor. In fact, archaeological sites show that humans actively hunted mammoths, and even a relatively small number of kills could have devastated populations that were already stressed by habitat loss. The reading overlooks the synergistic effect of climate and hunting. Second, the timing argument is flawed. In North America, for example, the arrival of the Clovis people around 13,000 years ago coincides almost exactly with the rapid extinction of mammoths. In Siberia, human populations expanded precisely during the warm intervals when mammoth numbers were dropping. This correlation strongly suggests that humans were the final push. Third, the genetic diversity decline cited in the reading can be explained by human hunting as well. If humans selectively killed large, healthy individuals, they could disrupt social structures and reduce breeding success, leading to genetic bottlenecks. Moreover, similar genetic declines have been observed in species known to be overhunted, such as the moa in New Zealand. Thus, the evidence does not uniquely support climate as the cause; human impact was likely decisive.
📝 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.
