The extinction of the woolly mammoth has long puzzled scientists, but a recent hypothesis proposes that a combination of rapid climate change and human overhunting was the primary cause. According to this view, the warming climate at the end of the Pleistocene dramatically reduced the mammoth's grassland habitat, fragmenting populations into isolated pockets. As these populations shrank, their genetic diversity declined, making them more vulnerable to diseases and reproductive failures. Meanwhile, human hunters, equipped with advanced weapons and organized strategies, systematically targeted mammoth herds, further accelerating their decline. Evidence cited includes the timing of mammoth extinction on different continents, which aligns with human arrival, and the discovery of mammoth bones with cut marks at archaeological sites. Additionally, climate models show that the shift from steppe-tundra to forest and peatland ecosystems drastically reduced the carrying capacity for large herbivores. Therefore, the interplay of environmental stress and hunting pressure, rather than any single factor, drove the species to extinction.
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The reading presents a neat story of climate and human hunting wiping out the mammoth, but the evidence suggests a more complex reality. First, the timing argument is flawed. In North America, mammoth populations persisted for thousands of years after the earliest human settlements, and some isolated populations survived on Wrangel Island until 2000 BC, long after climate had warmed and humans had arrived. This contradicts the claim that hunting was decisive. Second, the genetic diversity decline is overstated. Studies of ancient DNA from late-surviving mammoth populations show that even small groups maintained moderate genetic diversity, and they did not exhibit signs of inbreeding depression until very late, suggesting that fragmentation alone was not lethal. Third, the climate hypothesis ignores other possible causes, such as volcanic eruptions or asteroid impacts that triggered abrupt cooling events, like the Younger Dryas, which could have decimated mammoth habitats in a few decades, not gradually. In fact, pollen and sediment records indicate that the grassland-to-forest transition was patchy and non-linear, with pockets of suitable habitat remaining, yet mammoths disappeared even from these refugia. Therefore, the reading's neat cause-and-effect model fails to account for the full range of evidence.
📝 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.
