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 correlates closely with the end of the last Ice Age, when global temperatures rose dramatically. As the glaciers retreated, the open grasslands that mammoths depended on were replaced by dense forests and tundra, reducing their food supply. Second, genetic studies of mammoth remains show a severe population bottleneck around 20,000 years ago, well before humans reached North America in large numbers. This indicates that climate-induced habitat loss had already weakened the species. Third, human hunting, while present, was likely too sparse to cause extinction. Archaeological sites from the period contain few mammoth bones compared to other megafauna, suggesting that humans rarely hunted them. Therefore, the woolly mammoth’s disappearance was a consequence of natural climate shifts, not human activity.
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The lecture challenges the reading’s claim that climate change alone drove the woolly mammoth to extinction. While it is true that temperatures rose, the reading overlooks that mammoths had survived previous interglacial periods with similar warming. For instance, they persisted through the Eemian interglacial 125,000 years ago, when forests expanded just as much. Thus, habitat change alone cannot explain their final demise. Second, the genetic bottleneck mentioned in the reading actually occurred during a cold period, not a warm one, and it was followed by a recovery when climate became milder. This suggests that other factors, such as human hunting, pushed the population over the edge later. Third, the reading’s claim about sparse hunting is misleading. Recent excavations at Clovis sites in North America have uncovered mammoth kill sites with clear cut marks on bones, and new dating shows that human arrival coincided precisely with the last mammoth populations in each region. Moreover, even low-intensity hunting can be devastating for species with slow reproduction rates, like mammoths. Therefore, while climate may have stressed the species, human predation was the decisive factor that led to their extinction.
📝 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.
