การเขียนเชิงบูรณาการ TOEFL

📖 เนื้อเรื่อง

The extinction of the woolly mammoth has long been attributed to human hunting, but recent evidence suggests that climate change was the primary driver. First, the warming period at the end of the last Ice Age (approximately 10,000 years ago) drastically reduced the mammoth’s grassland habitat. As temperatures rose, forests and peatlands expanded, fragmenting the steppe-tundra ecosystem that mammoths depended on. This habitat loss would have made it impossible for large populations to survive, regardless of human activity. Second, the extinction timeline does not align with human expansion. Mammoth populations persisted on isolated islands, such as Wrangel Island, until around 4,000 years ago, long after humans had migrated to mainland Siberia and North America. If hunting were the main cause, these island populations would likely have been wiped out earlier. Third, genetic evidence from mammoth remains shows a significant decline in genetic diversity just before extinction, indicating small, isolated populations that were vulnerable to inbreeding and disease. This pattern is typical of populations stressed by environmental change, not by efficient predators. Therefore, the woolly mammoth’s demise was a result of natural climate shifts, not overhunting by early humans.

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The reading’s claim that climate change alone drove mammoth extinction is not convincing. First, while habitat loss was real, humans accelerated the process by setting fires to manage landscapes and by hunting megafauna, which reduced the grazing pressure that maintained grasslands. Without mammoths and other large herbivores, grasslands became scrublands, creating a feedback loop that worsened habitat loss—so human involvement was indirect but crucial. Second, the survival of mammoths on Wrangel Island until 4,000 years ago actually supports the hunting hypothesis. Mainland mammoths went extinct earlier because they were accessible to humans, whereas island populations were isolated and thus protected from initial hunting. When humans finally reached Wrangel Island, the mammoths disappeared within a few centuries—a pattern consistent with a hunting-driven extinction. Third, the loss of genetic diversity cited in the reading can be explained by human hunting, not just climate. Hunting selectively removes the largest individuals, often the most genetically diverse, and can cause population bottlenecks. Climate change would have caused more gradual genetic erosion, not the sudden decline observed. In sum, the evidence points to humans as the decisive factor, with climate as only a background stressor.