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, megafauna disappeared shortly after the Clovis people crossed the Bering land bridge around 13,000 years ago. Similarly, in Australia, the arrival of humans about 45,000 years ago coincided with the loss of giant marsupials. Second, archaeological evidence supports the overhunting hypothesis. Clovis spear points have been found embedded in the bones of mammoths and other large prey, indicating that humans actively hunted these animals. Moreover, kill sites show that early humans targeted juveniles and females, which would have devastated populations. Third, the megafauna species that went extinct were those most vulnerable to hunting—large, slow-reproducing animals with long gestation periods. In contrast, smaller, faster-reproducing species survived, suggesting that human predation, rather than climate change, was the selective pressure. Climate change, while occurring, was not unique to this period and had occurred many times before without causing such selective extinctions. Therefore, human hunting is the primary cause of the megafauna extinction.
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The reading argues that human overhunting drove megafauna extinction, but this view is flawed. First, the correlation between human arrival and extinction is not as clear as claimed. In North America, some megafauna species, such as the giant short-faced bear, disappeared thousands of years before Clovis people arrived, while others survived long after. In Australia, the timing is also uncertain; some extinctions occurred before humans arrived, and others after, making a simple cause-and-effect relationship untenable. Second, the archaeological evidence is overstated. While spear points have been found with bones, these could represent scavenging rather than active hunting. Humans may have used tools to cut meat from animals that died of natural causes, such as disease or accidents. Additionally, the number of confirmed kill sites is extremely small—only a few dozen worldwide—which is insufficient to explain the extinction of millions of animals across continents. Third, the vulnerability argument ignores climate and environmental changes. The Pleistocene-Holocene transition brought dramatic shifts in temperature and vegetation, fragmenting habitats and reducing food sources for large herbivores. This would have stressed megafauna populations, making them more susceptible to any additional pressure, including modest hunting. Moreover, many extinct species, such as giant ground sloths, were not likely primary prey for humans, yet they disappeared. Thus, a combination of climate change and habitat loss, not human overhunting, is a more plausible explanation.
📝 작문 지시 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).
