Escritura integrada TOEFL

📖 Texto de lectura

The extinction of the woolly mammoth has long been attributed to overhunting by early humans, but recent evidence suggests that climate change was the primary driver. First, the timing of mammoth extinctions aligns closely with major climatic shifts. Radiocarbon dating shows that most mammoth populations disappeared during the Bølling-Allerød warming period, about 14,000 years ago, when temperatures rose rapidly and dramatically. Human hunting pressure, in contrast, had been present for millennia without causing extinction. Second, the geographic pattern of extinction supports a climate-based explanation. Mammoths survived longest in isolated refugia such as Wrangel Island and the Taymyr Peninsula, where cooler conditions persisted. If humans were the main cause, we would expect extinction to occur first in areas with high human population density, such as the Eurasian steppe, but the opposite is observed. Third, the diet of mammoths was highly specialized. Stable isotope analyses of mammoth collagen show they relied on cold-adapted grasses and sedges, which thrived in the dry, cold steppe. As the climate warmed and became wetter, these plants were replaced by shrubs and forests, depriving mammoths of their primary food source. The loss of suitable habitat and food supply, not human hunting, best explains their decline.

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The reading's claim that climate change alone drove mammoth extinction is unconvincing. While it is true that temperatures rose rapidly 14,000 years ago, note that mammoths had survived many previous warming events, such as the Eemian interglacial about 120,000 years ago, without going extinct. So why did they fail to adapt this time? The difference is the presence of highly efficient human hunters. Second, the survival of mammoths on Wrangel Island actually supports human hunting as a key factor. Wrangel Island was not a climatic refuge—it was simply too small and too remote for humans to reach easily. In contrast, on the mainland, where humans had ready access, mammoths vanished quickly. Moreover, the island populations were dwarfed and genetically bottlenecked, suggesting they were stressed and vulnerable, not thriving. Third, the dietary evidence is misleading. Isotope data show that mammoths were not strict specialists; they could consume a wide range of vegetation, including shrubs and even tree bark. In fact, during the warmer periods, woolly mammoths on the mainland shifted their diets successfully. What changed was not the availability of plants, but the arrival of spear-wielding hunters who targeted juvenile and female mammoths, as evidenced by kill sites with butchery marks. Thus, while climate may have stressed populations, it was human predation that delivered the final blow.