Escritura integrada TOEFL

📖 Texto de lectura

The extinction of the woolly mammoth has long been attributed to human overhunting, but a closer examination of the fossil record and ancient DNA suggests that climate change was the primary driver. First, the timing of mammoth extinctions aligns with major climatic shifts, not with human expansion. Radiocarbon dating shows that mammoth populations dwindled dramatically during the Last Glacial Maximum (about 20,000 years ago) and then again during the Younger Dryas (about 12,000 years ago), both periods of rapid warming and vegetation change. In contrast, human hunters had already been present in Siberia and North America for millennia before these declines, yet mammoth numbers remained stable until the climate shifted. Second, climate change altered the mammoth’s habitat. Mammoths depended on the ‘mammoth steppe’—a dry, grassy plain that covered much of the Arctic. As temperatures rose, this steppe was replaced by wet tundra and boreal forest, which offered poor forage. Pollen records from lake sediments indicate that the spread of shrubs and trees coincided with mammoth population crashes, while human hunting pressure showed no such correlation. Third, genetic evidence reveals that mammoth populations suffered from reduced genetic diversity before their final extinction, a sign of environmental stress rather than hunting. Isolated populations on Wrangel Island and St. Paul Island survived for thousands of years after humans arrived in their regions, but they eventually died out during periods of abrupt climate change, suggesting that even without hunting, climate alone could drive them to extinction.

🎧 Conferencia de audio

The reading’s claims are plausible but overlook key evidence that supports human hunting as the decisive factor. First, the timing argument is flawed. While mammoth populations did decline during warming periods, the most severe and final extinctions occurred after humans arrived with advanced hunting technologies, such as the Clovis points in North America. In Eurasia, mammoth bones with embedded spear points and butchery marks date to the exact period of their disappearance, whereas climate shifts alone cannot explain why mammoths survived earlier interglacial warmings that were just as severe. Second, the habitat change argument is overstated. Climate change did alter vegetation, but mammoths were adaptable grazers that could have shifted their range. In fact, fossil evidence shows that mammoths thrived in partially forested areas during earlier warm periods. What they could not adapt to was the relentless hunting pressure from growing human populations, which targeted their herds and disrupted their social structure. Third, the genetic diversity argument actually supports hunting, not climate. The low genetic diversity seen in late populations is a classic signature of a small, stressed population, but this stress was likely caused by overhunting, which reduced populations to critical levels. On Wrangel Island, mammoths survived until about 4,000 years ago, but their extinction coincided with the arrival of human settlers, not with a unique climatic event—climate records show no dramatic change at that time. Thus, when humans arrived, the end was inevitable.