The extinction of the large-bodied mammals, such as mammoths and giant ground sloths, at the end of the Pleistocene has long puzzled scientists. While climate change is often cited as a factor, the most compelling explanation is overhunting by early humans. First, the timing of these extinctions correlates with human migration. In North America, megafauna disappeared roughly 13,000 years ago, soon after the arrival of the Clovis people, whose distinctive spear points are found at kill sites. Second, megafauna were particularly vulnerable to hunting due to their slow reproductive rates. Species like mammoths had long gestation periods and produced few offspring, making them unable to recover from even modest hunting pressure. Third, archaeological evidence shows that humans had the technology and organization to hunt large animals. Clovis points, crafted from stone, were effective weapons, and kill sites with butchered remains confirm that these tools were used on megafauna. Thus, human predation, not climate, drove these species to extinction.
🎧 听力讲座
🎯 模拟考试环境：先点「播放讲座」听完内容，再作答。听力原文默认隐藏。
The lecture challenges the overhunting hypothesis, arguing that it fails to account for key evidence. First, the timing argument is flawed. In many regions, such as South America and Australia, megafauna extinctions occurred thousands of years before or after human arrival. For example, in Australia, giant marsupials disappeared about 45,000 years ago, but humans arrived much earlier, around 60,000 years ago, leaving a gap inconsistent with immediate overkill. Second, while slow reproduction made megafauna vulnerable, studies of modern elephant populations—close relatives of mammoths—show that they can sustain low levels of hunting. Moreover, the human population at that time was too small to exert sufficient pressure, given that megafauna were vast in number. Third, the archaeological evidence is weak. Clovis points are rare, and kill sites are scarce; many sites show signs of scavenging, not active hunting. Also, some megafauna species lacked natural predators and were not adapted to flee humans, but this would not guarantee successful kills. The lecture concludes that climate shifts, which altered habitats and food sources, better explain the pattern of extinction.
📝 Writing Prompt Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
📊 TOEFL Integrated Writing Rubric
Content Accuracy: Accurately capture the relationship between lecture and reading
Information Completeness: Cover all key counter-arguments from the lecture
Structure & Coherence: Logical organization and progression
Language Use: Grammar, vocabulary, expression accuracy
Scored 0-30 based on holistic scoring (original 0-5, scaled to 30).
