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 extinction coincides with the end of the last Ice Age, when global temperatures rose rapidly. As forests expanded and grasslands shrank, the mammoth’s open-steppe habitat disappeared, reducing food availability. Second, archaeological sites show that human hunting of mammoths was relatively rare—only a few kill sites have been found, and most contain only one or two animals, suggesting that hunting was opportunistic and not intensive enough to drive a species to extinction. Third, genetic studies of ancient mammoth remains reveal a dramatic decline in genetic diversity thousands of years before their final disappearance. Low genetic diversity would have made them vulnerable to disease and inbreeding depression, which is more consistent with a slow environmental decline than with sudden human overkill.

🎧 Conferencia de audio

The arguments for climate change as the main cause of mammoth extinction are not convincing. First, although the climate did warm, large areas of suitable habitat—such as the mammoth steppe—persisted in parts of Siberia and Alaska until much later, and mammoths survived there for thousands of years after the warming began. This suggests that habitat loss alone cannot explain their extinction. Second, the claim that human hunting was rare is misleading. Many kill sites have been discovered, but they are often poorly preserved because bones were scattered or used by humans. Moreover, even low-intensity hunting can have a devastating impact on slow-reproducing species like mammoths, which had long gestation periods and few offspring. Third, the genetic diversity decline cited in the reading may actually be a result of human hunting, not climate. When human populations expanded and began hunting mammoths, they fragmented the populations and reduced their numbers, leading to inbreeding and loss of genetic variation. Therefore, the genetic evidence does not contradict the overhunting hypothesis—it supports it.