托福综合写作

📖 阅读文章

The Extinction of the Megafauna: A Human-Driven Phenomenon The disappearance of large terrestrial mammals, such as woolly mammoths, giant sloths, and saber-toothed cats, at the end of the Pleistocene epoch has long puzzled scientists. While some argue for climate change as the primary cause, a growing body of evidence points to human overhunting as the decisive factor. First, the timing of extinctions correlates strongly with the arrival of modern humans on different continents. In North America, for example, the megafauna disappeared roughly 13,000 years ago, coinciding with the spread of the Clovis culture, whose distinctive spear points are found at kill sites. Second, the selectivity of extinction supports human hunting: species that were large, slow-reproducing, and easy to target—such as mammoths and ground sloths—suffered disproportionately, whereas smaller, faster-breeding animals survived. Third, ecological modeling demonstrates that even a modest human population, with a preference for hunting large prey, could drive such species to extinction within a few centuries, especially when combined with habitat fragmentation caused by human settlement. These patterns, consistent across continents and independent of climate shifts, strongly suggest that human activity, not natural environmental change, was the primary driver of this ancient mass extinction.

🎧 听力讲座

The professor challenges the reading's claim that humans caused the megafauna extinction. Let's examine the points. First, the correlation between human arrival and extinction is not as tight as claimed. In Australia, megafauna disappeared about 46,000 years ago, which is roughly 10,000 years after the first human colonization, and in some regions, humans coexisted with large mammals for millennia before extinction. This timing lag weakens the direct-hunting hypothesis. Second, the selectivity argument is flawed. Climate change during the Pleistocene was dramatic, with rapid temperature swings and vegetation shifts. Species like mammoths, which required vast grasslands, would have been particularly vulnerable to the spread of forests and the loss of their habitat. In fact, fossil evidence shows that many megafauna species experienced population declines and range contractions before humans even arrived in those areas, indicating that environmental stress had already taken a toll. Third, the modeling studies are overly simplistic; they assume constant human hunting pressure and ignore other factors such as disease, which could have been introduced by humans or their domesticated animals. Moreover, recent archaeological findings show that early humans often scavenged rather than hunted, and many kill sites attributed to humans may actually be cases where humans butchered already dead animals. Thus, the evidence for human-driven extinction is far from conclusive, and climate change remains a more plausible explanation.