TOEFL Integrated Writing

📖 Reading Passage

The extinction of large mammals during the late Pleistocene, often attributed to human overhunting, may have been primarily caused by climate change. First, the timing of extinctions correlates more closely with rapid climate shifts than with human arrival. For instance, in North America, many megafauna species disappeared around 13,000 years ago, a period of dramatic temperature and vegetation changes, whereas humans had arrived earlier. Second, climate change would have reduced the availability of essential habitats. Warmer and drier conditions shrank grasslands and expanded forests, diminishing the open habitats that mammoths, horses, and other grazers depended on, leading to food shortages and population declines. Third, some megafauna species that survived, such as bison and moose, were more adaptable to diverse environments, while those that went extinct were often specialized feeders with narrow ecological niches, making them more vulnerable to habitat disruption. Thus, the evidence suggests that climate-driven environmental changes, not human hunting, were the decisive factor in these extinctions.

🎧 Listening Lecture

The reading’s argument that climate change caused megafauna extinctions is unconvincing. While climate shifts did occur, they were not unique—similar fluctuations happened earlier without causing mass extinctions. In contrast, human arrival in North America around 14,000 years ago coincides with a wave of extinctions, and in places like New Zealand and Madagascar, megafauna disappeared soon after humans arrived, even though climate was stable. Second, the habitat change theory overlooks that many megafauna species were highly mobile and could migrate to suitable areas. For example, woolly mammoths moved across vast ranges, so shrinking grasslands alone would not have wiped them out. Third, the reading’s claim about specialized feeders is misleading—many extinct species, like the giant ground sloth, were generalist herbivores that could eat various plants. Furthermore, archaeological sites show clear evidence of hunting, including butchering marks on mammoth bones and Clovis spear points, which directly implicates humans. Thus, overhunting, not climate, drove these extinctions.