The extinction of the woolly mammoth, a species that roamed the Earth during the last Ice Age, has long puzzled scientists. While many attribute their disappearance to human hunting, recent studies suggest that climate change was the primary driver. Three key arguments support this view. First, the warming climate at the end of the Pleistocene drastically reduced the mammoth’s habitat. As glaciers retreated, the vast steppe-tundra, which provided their main food source, was replaced by forests and wetlands, forcing mammoths into smaller, isolated areas where they struggled to survive. Second, genetic evidence from fossil remains shows a significant decline in genetic diversity starting around 20,000 years ago, well before humans developed advanced hunting tools. This bottleneck suggests that populations were already shrinking due to environmental stress, not overhunting. Third, the timing of extinction varies by region, correlating with local climatic shifts rather than human arrival. For example, mammoths survived on Wrangel Island until 2000 BCE, long after humans had settled nearby, but the island’s vegetation changed dramatically as the climate became wetter, making it unsustainable. Thus, climate change, not human predation, was the decisive factor in the mammoth’s demise.
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The reading’s argument that climate change alone drove woolly mammoth extinction is not convincing. While climate did alter their habitat, human hunting was a far more critical factor. First, the habitat reduction theory overlooks the fact that mammoths were highly adaptable. Fossil pollen records show that they could thrive in varied environments, including shrub tundra and even boreal forests, as long as prey densities were low. The decline in suitable steppe-tundra did not necessarily mean starvation; rather, it forced mammoths into concentrated areas where they became easier targets for human hunters. Second, the genetic bottleneck cited in the reading actually supports the hunting hypothesis. A decline in diversity often results from a population being fragmented by human hunting pressure, not just climate. Moreover, archaeological sites from 15,000 years ago show mammoth bones with clear butchering marks, indicating that humans actively hunted them. Third, the Wrangel Island example is misleading. Humans did not settle there until 2000 BCE, but the mammoth population was already tiny and genetically isolated; a sudden disease or extreme weather event could have finished them off. In contrast, on the mainland, where humans arrived earlier, mammoths vanished quickly, suggesting that hunting, not gradual climate change, was the killing blow. Therefore, the evidence points to human activity as the primary cause, with climate playing 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.
