The extinction of the megafauna—large animals such as woolly mammoths, giant ground 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 human populations. First, the timing of extinctions aligns closely with human migration. In North America, for example, the arrival of Clovis hunters around 13,000 years ago coincides with the rapid disappearance of nearly 35 genera of large mammals. Second, archaeological evidence supports human predation. At sites like the Murray Springs Clovis site in Arizona, researchers have found spear points embedded in mammoth skeletons, along with butchering tools, indicating that humans actively hunted these animals. Third, the selectivity of extinction—favoring large-bodied species with slow reproductive rates—matches the pattern expected from human hunting pressure, as these animals would be particularly vulnerable to even modest levels of additional mortality. In contrast, climate change at the end of the last ice age, while significant, affected both large and small species and occurred gradually over millennia, failing to explain the sudden, size-selective losses. Therefore, human overhunting stands as 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 argument that human overhunting caused megafaunal extinction is not convincing. First, the timing argument is flawed. In many regions, such as South America and Australia, megafaunal extinctions occurred thousands of years before humans arrived. For instance, in Australia, giant marsupials disappeared around 46,000 years ago, but human colonization is dated to only 50,000 years ago—and recent evidence suggests humans may have arrived even later, after the extinctions. Second, the archaeological evidence is ambiguous. At sites like Murray Springs, the association between spear points and mammoth remains is debated; some bones show no cut marks, and the spear points may have been deposited separately, possibly washed in by water. Moreover, if hunting were the main cause, we would expect far more kill sites given the presumed abundance of humans and animals, yet such sites are extremely rare. Third, the selectivity argument actually supports climate change. Large animals have lower reproductive rates, making them more sensitive to environmental disruptions that reduce food quality or habitat. The Pleistocene-Holocene transition brought rapid warming and vegetation shifts, which would disproportionately affect large herbivores and, in turn, their predators. In fact, extinctions peaked during abrupt climate oscillations, not immediately after human arrival. Thus, climate change, not hunting, best explains the pattern.
📝 Инструкция по письму 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).
