การเขียนเชิงบูรณาการ TOEFL

📖 เนื้อเรื่อง

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 declines correlates more closely with rapid warming events than with human migration patterns. Paleoclimatic data show that mammoth populations collapsed during the Pleistocene-Holocene transition (around 11,000 years ago), a period of significant temperature rise, whereas human hunters had already inhabited Siberia for thousands of years without causing major declines. Second, mammoths were highly specialized for cold, dry steppe environments. As the climate warmed, forests and wetlands expanded, fragmenting their habitat and reducing their primary food sources—grasses and sedges. This habitat loss would have made populations vulnerable regardless of hunting pressure. Third, genetic studies of ancient mammoth remains reveal a loss of genetic diversity and an increase in harmful mutations in their final millennia, indicating small, isolated populations struggling to adapt to environmental stress. Such genetic deterioration is more consistent with climate-induced habitat fragmentation than with a sudden overkill by humans, which would have left a different genetic signature.

🎧 การบรรยาย

The reading's argument that climate change alone drove mammoth extinction is flawed. While warming did alter habitats, human hunting was the decisive factor that pushed already stressed populations over the edge. First, the correlation between warming and decline is not as clean as claimed. Mammoths survived previous interglacial warm periods, such as the Eemian, without going extinct. What was different in the late Pleistocene was the arrival of highly efficient human hunters with advanced weapons. Second, habitat fragmentation alone cannot explain extinction because mammoths were highly adaptable. Fossil evidence shows they shifted their diets and moved to refugia, such as northern islands, where they persisted for thousands of years after the mainland warming. Those island populations only disappeared when humans arrived, not when climate changed. Third, the genetic evidence actually supports human involvement. The small, isolated populations with low genetic diversity that the reading cites were likely the result of hunting reducing populations to tiny pockets, not climate fragmentation. Moreover, when humans reached islands like Wrangel, they hunted the last mammoths, leaving a genetic bottleneck that matches an overkill scenario. In sum, hunting was the coup de grâce that climate change alone could not deliver.