托福综合写作

📖 阅读文章

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 coincides with the end of the last Ice Age, when global temperatures rose dramatically. Paleoclimatic data show that mammoth populations began shrinking around 15,000 years ago, well before humans developed advanced hunting tools. Second, mammoths were highly adapted to cold, dry steppe environments. As the climate warmed, forests and wetlands expanded, fragmenting their habitats and reducing their food sources. This would have made survival increasingly difficult regardless of human activity. Third, genetic studies of mammoth remains reveal a loss of genetic diversity in the final millennia, a classic sign of population stress from environmental change, not from hunting pressure, which tends to leave a different genetic signature. Therefore, although humans may have delivered the final blow, climate-induced habitat loss was the fundamental cause of the mammoth's extinction.

🎧 听力讲座

The lecture challenges the reading's claim that climate change was the main cause of woolly mammoth extinction. While the timing of warming does correlate with mammoth decline, this does not prove causation. In fact, mammoths survived similar warming periods in earlier interglacial epochs without going extinct, so climate alone cannot explain their disappearance. The habitat fragmentation argument also has weaknesses. Fossil evidence shows that mammoths were flexible eaters, capable of consuming a variety of plants, including grasses, sedges, and even shrubs from forest margins. They were not strictly dependent on steppe vegetation, so the expansion of forests would not have been fatal. Finally, the genetic diversity argument is misleading. The loss of genetic diversity observed in late mammoth populations is consistent with a rapid population crash, which is more typical of overhunting by humans. When humans arrived in Siberia and North America, they hunted mammoths intensively, and the sudden removal of individuals would reduce genetic variation quickly. In contrast, gradual climate change would allow for more gradual genetic drift. Thus, the evidence points to human hunting as the decisive factor, not climate.