Escritura integrada TOEFL

📖 Texto de lectura

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 extinctions correlates more closely with climatic shifts than with human arrival. In North America, mammoths disappeared around 10,000 years ago, coinciding with the end of the last Ice Age and a rapid warming event, whereas humans had been present for at least 2,000 years prior without causing extinction. Second, paleoclimatic data show that warming reduced the mammoth’s preferred habitat—cold steppe grasslands—by up to 90% in some regions. As these grasslands were replaced by forests and wetlands, mammoths faced food scarcity and fragmentation of their populations. Third, genetic studies of mammoth remains reveal a decline in genetic diversity during the final millennia, indicating small, isolated populations that were vulnerable to stochastic events like disease or extreme weather, rather than sustained hunting pressure. Thus, climate-driven habitat loss, not human hunting, was the decisive factor in the mammoth’s demise.

🎧 Conferencia de audio

The professor challenges the reading’s claim that climate change alone drove the woolly mammoth to extinction. While acknowledging that climate played a role, she argues that human hunting was the critical factor. First, she points out that the correlation between warming and extinction is not as tight as the reading suggests. For example, mammoths survived on Wrangel Island for thousands of years after the warming event, persisting until about 4,000 years ago—long after the climate had stabilized to conditions similar to those in earlier times. This contradicts the idea that warming alone was fatal. Second, the professor notes that the loss of steppe grasslands did not necessarily mean starvation. Mammoths were generalist feeders; analyses of their dung and dental remains show they could adapt to a wider diet, including shrubs and tree bark. In fact, populations in some areas thrived in forested environments, indicating that habitat change alone was not a limiting factor. Third, she argues that the genetic bottleneck observed in late mammoth populations is more consistent with overhunting. When humans arrived on Wrangel Island, they likely hunted the small, isolated herds to extinction quickly, leaving a genetic signature of a sudden population crash. In contrast, climate-driven decline would produce a more gradual loss of diversity. Therefore, human predation, especially on remnant populations, was the ultimate cause of extinction.