การเขียนเชิงบูรณาการ TOEFL

📖 เนื้อเรื่อง

The extinction of the woolly mammoth has long been attributed to overhunting by early humans. However, recent evidence suggests that climate change was the primary driver. Proponents of the climate theory cite three main arguments. First, the warming at the end of the Pleistocene reduced the mammoth's preferred habitat—cold, dry grasslands—by replacing them with forests and wetlands, which offered less forage and increased predation risk. Second, the timing of extinction correlates more closely with rapid climate shifts, such as the Younger Dryas and the subsequent Holocene warming, than with human migration patterns. For example, mammoths survived on isolated islands like Wrangel Island long after humans arrived, but they disappeared soon after abrupt climate events. Third, genetic studies of ancient mammoth remains show a decline in genetic diversity and fitness—such as smaller body size and reduced fertility—that is typical of populations stressed by environmental change, not by hunting pressure. These factors—habitat loss, temporal correlation, and genetic degradation—collectively indicate that climate change, not human hunting, caused the mammoth's demise.

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The lecture challenges the reading's claim that climate change alone drove woolly mammoth extinction. While habitat changes did occur, they were not as uniform or catastrophic as the reading suggests. In many regions, suitable grassland patches persisted, and mammoths could adapt by shifting ranges, as evidenced by their survival in Beringia until later periods. Second, the timing argument is flawed: human arrival in North America and Eurasia often precedes mammoth decline by centuries, but archaeological sites with mammoth kill sites and tool marks show intense hunting exactly when populations crashed. Moreover, on Wrangel Island, mammoths survived for thousands of years after climate stabilized, only to vanish around 4,000 years ago—when humans first arrived there by boat. Third, the genetic data cited actually supports human hunting: reduced genetic diversity can result from a population bottleneck caused by rapid overhunting, not just climate stress. In fact, similar genetic patterns are seen in other megafauna that were clearly hunted to extinction, such as the giant ground sloth. Thus, the reading's reliance on climate overlooks the strong evidence that human predation was the decisive factor.