TOEFL Integrated Writing

📖 Reading Passage

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 decline correlates with the warming period at the end of the last Ice Age, not with human expansion. Radiocarbon dating shows that mammoth populations collapsed between 15,000 and 10,000 years ago, a period when temperatures rose dramatically, while human hunters had already been present in Eurasia for thousands of years without causing significant decline. Second, mammoths were adapted to cold, dry steppe environments. As the climate warmed, forests and wetlands replaced grasslands, fragmenting their habitat and reducing their food supply. Fossil pollen records indicate a rapid shift in vegetation, which would have made it difficult for mammoths to find sufficient forage. Third, isolation on small islands, such as Wrangel Island, led to genetic problems. With rising sea levels, mammoths became trapped on islands where inbreeding and reduced genetic diversity weakened their ability to survive, even without human interference. These factors point to climate as the main cause of their extinction.

🎧 Listening Lecture

The reading's claims about climate change are not convincing. First, the timing argument is flawed. While warming began 15,000 years ago, mammoths survived on mainland Siberia until about 10,000 years ago, and on Wrangel Island until 4,000 years ago. This suggests they could adapt to warmer conditions, so why did they disappear exactly when human populations expanded into their last refuges? Second, the vegetation change was not uniform. In many areas, mammoths coexisted with shrubs and forests, and their diet was more flexible than assumed. Coprolite (fossil dung) analysis shows they ate a variety of plants, including woody species. Thus, habitat change alone cannot explain their extinction. Third, the island dwarfing and genetic issues were consequences, not causes, of small populations. In fact, genetic studies of Wrangel Island mammoths show they persisted for thousands of years despite low diversity, indicating they could survive inbreeding. The real factor was likely hunting by humans, who arrived on these islands and killed the last survivors. Therefore, the reading's climate hypothesis fails to account for the full evidence.