TOEFL Integrated Writing

📖 Reading Passage

The extinction of the woolly mammoth has long been attributed to human overhunting. However, a more nuanced explanation involves a combination of climate change and genetic factors. First, climate warming at the end of the Pleistocene reduced the mammoth’s preferred habitat—cold, dry grasslands—by allowing forests and wetlands to expand, fragmenting populations. Second, as populations became isolated, inbreeding and reduced genetic diversity led to lower fertility and increased susceptibility to disease. Third, the arrival of humans with advanced hunting tools may have delivered the final blow to already stressed populations, but climate was the primary driver. Evidence from fossil pollen shows that vegetation shifts coincided with mammoth declines, and DNA from late-surviving populations on Wrangel Island reveals low genetic diversity. Thus, while humans played a role, the ultimate cause was environmental change.

🎧 Listening Lecture

The reading’s claim that climate change was the primary cause of mammoth extinction is not well supported. First, the vegetation shift argument is flawed. In many regions, mammoths coexisted with forests and wetlands for thousands of years, and they were not strictly dependent on grasslands; they could adapt to varied diets. Second, the genetic evidence from Wrangel Island is misleading. The low genetic diversity found there occurred after the population had already been small for centuries, and it did not necessarily cause extinction—those mammoths survived for over 5,000 years after the main extinction event. Third, the role of humans is underestimated. Archaeological sites show clear evidence of mammoth hunting, and the timing of human arrival in Siberia and North America correlates with rapid mammoth declines, even in areas where climate remained stable. In fact, on islands where humans never arrived, mammoths persisted until much later. Therefore, overhunting, not climate, best explains the pattern of extinction.