The extinction of the megafauna—large animals such as mammoths, giant sloths, and saber-toothed cats—at the end of the Pleistocene epoch has long puzzled scientists. While many factors have been proposed, the most compelling explanation is overhunting by early humans. First, the timing of extinctions correlates strongly with human arrival on different continents. In North America, for example, the disappearance of megafauna occurred roughly 13,000 years ago, shortly after the Clovis people crossed the Bering land bridge. Similarly, in Australia, giant marsupials vanished around 46,000 years ago, coinciding with the arrival of Aboriginal settlers. Second, the megafauna that went extinct were particularly vulnerable to hunting due to their large size and slow reproductive rates. Unlike smaller animals, these species produced few offspring and had long gestation periods, making it impossible for populations to recover from sustained hunting pressure. Third, archaeological evidence supports human predation. At sites like the Clovis type site in New Mexico, spear points have been found embedded in mammoth skeletons, and cut marks on bones indicate butchering. Such evidence demonstrates that humans actively hunted these animals, not merely scavenged them. Therefore, human overhunting is the primary driver of megafaunal 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 reading's claim that human overhunting caused megafaunal extinction is problematic. While the timing correlation is intriguing, it fails to account for climate change. During the Pleistocene-Holocene transition, rapid warming and shifts in vegetation transformed habitats. In many regions, megafauna declined before or after human arrival, not with it. For instance, in Eurasia, woolly mammoths survived until 4,000 years ago on Wrangel Island, long after humans had settled nearby, yet they eventually vanished due to shrinking grassland habitats. Second, the vulnerability argument is oversimplified. Many extinct megafauna, like mammoths, had large body sizes that actually reduced predation risk, and their reproductive rates, while low, were sufficient in stable environments. The real issue was habitat fragmentation, which disrupted their breeding and feeding patterns. Third, the archaeological evidence is ambiguous. While some kill sites exist, they are rare and often show signs of scavenging rather than active hunting. For example, many mammoth bones with cut marks may have been from animals that died naturally, and humans merely processed the carcasses. Moreover, if overhunting were the cause, we would expect to see mass kill sites, but these are absent. Therefore, climate change, not human hunting, best explains the megafaunal extinctions.
📝 Hướng dẫn viết 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).
