TOEFL Integrated Writing

📖 Reading Passage

The extinction of the woolly mammoth has long been attributed to human hunting, but recent evidence suggests that climate change was the primary driver. First, the timing of mammoth extinction correlates with the end of the last Ice Age, when temperatures rose dramatically. Paleoclimate data show that mammoths disappeared from mainland Siberia and North America around 10,000 years ago, exactly when forests replaced grasslands. These grasslands, which provided mammoths with their main food source, shrank as warmer, wetter conditions allowed trees to spread. Second, genetic studies of mammoth remains reveal a severe population bottleneck long before humans arrived in large numbers. DNA analysis indicates that mammoth populations declined sharply about 20,000 years ago, during a period of intense cold, not during periods of human expansion. This suggests that climate stress, not hunting, weakened the species. Third, human hunting was likely too sparse to cause extinction. Archaeological sites with mammoth bones are rare, and the estimated human population in Siberia at that time was only a few thousand, far too small to overhunt a widespread species. Thus, climate-driven habitat loss and population stress are more plausible explanations than human predation.

🎧 Listening Lecture

The reading's claim that climate change killed the mammoths is flawed. First, the correlation between warming and extinction is weak. Mammoths survived previous interglacial warm periods, such as the Eemian around 120,000 years ago, when forests also expanded. If climate alone were the cause, they would have gone extinct then, but they didn't. Second, the genetic bottleneck cited in the reading is actually evidence for human impact, not against it. The decline starting 20,000 years ago coincides with the first appearance of humans in the Arctic, not with a climate event. Humans may have hunted mammoths gradually, reducing populations long before the final extinction. Third, the rarity of mammoth bones at archaeological sites is misleading. Many mammoth carcasses were scavenged or used for building materials, so bones were not left at kill sites. Moreover, even a small human population could have driven mammoths to extinction by targeting calves or pregnant females, which would have a disproportionate effect on population growth. Therefore, the lecture shows that human hunting remains a viable explanation, and the reading's climate-only theory is not supported.