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 human migration correlates strongly with megafaunal extinctions. 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 the hunting hypothesis. At sites like Murray Springs in Arizona, scientists have found spear points embedded in mammoth skeletons, alongside butchering tools. This direct evidence indicates that humans actively hunted these animals, not merely scavenged their remains. Third, the selective extinction pattern favors human hunting. Megafauna species that went extinct were generally large, slow-reproducing, and naive to human predators, making them easy targets. In contrast, smaller, faster-reproducing species survived. This pattern is consistent with a human-induced overkill, as these traits would make populations vulnerable to sustained hunting pressure. Although some scientists argue that climate change was responsible, the abruptness and selectivity of the extinctions—occurring at different times on different continents, always just after human arrival—strongly implicate human activity as the primary driver.
🎧 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 argues that human overhunting caused megafaunal extinctions, but this view is overly simplistic and contradicted by evidence. First, the timing correlation is not as clean as the reading suggests. In many regions, such as Australia and South America, megafauna disappeared thousands of years before or after human arrival, with gaps of up to several millennia. This weakens the claim that human presence alone triggered extinctions. Second, the archaeological evidence cited is actually rare and ambiguous. While some kill sites exist, they are few compared to the vast number of megafaunal fossils. Moreover, many of these 'kill sites' could represent scavenging, where humans used carcasses of animals that died from other causes. The presence of tools does not prove active hunting. Third, the selective extinction pattern can be better explained by climate change. Large animals have lower population densities and longer generation times, making them more vulnerable to environmental shifts, such as altered vegetation and drought. In fact, periods of rapid climate change, like the Younger Dryas, coincide with extinction pulses even in areas without human hunters. Thus, while humans may have contributed locally, the evidence points to climate as the primary driver of megafaunal demise.
📝 คำแนะนำการเขียน 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).
