托福综合写作

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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 closely correlates with human migration. In North America, for example, megafauna disappeared shortly after the arrival of Clovis hunters around 13,000 years ago, and in Australia, extinctions followed human colonization about 45,000 years ago. Second, archaeological evidence supports human predation. Kill sites with spear points embedded in megafauna bones, such as the famous Clovis points found with mammoth remains, demonstrate that humans actively hunted these animals. Third, the selectivity of extinction favors the overhunting hypothesis. Species that went extinct were typically large-bodied and slow-reproducing, making them vulnerable to hunting pressure, while smaller, faster-reproducing species survived. In contrast, climate change at the end of the Ice Age would have affected all species equally, not just the large ones. Therefore, human hunting, not climate, was the primary driver of megafaunal extinction.

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The reading's claim that human overhunting caused megafaunal extinction is problematic. First, the timing correlation is not as clear as suggested. In Eurasia, many megafauna species, such as woolly rhinos, disappeared before humans arrived in significant numbers, and in Africa, where humans evolved, megafauna persisted despite long-term hunting. Thus, human arrival alone cannot explain the pattern. Second, the archaeological evidence is far from conclusive. Kill sites are extremely rare and often ambiguous—many so-called kill sites may represent scavenging, where humans butchered animals that had died of natural causes. For every site with spear points, there are dozens of megafauna fossils with no sign of human interaction. Third, the selectivity argument is flawed because climate change can also be selective. Large animals have lower population densities and longer gestation periods, making them more vulnerable to environmental stress, such as habitat fragmentation and reduced food supply. In fact, the last glacial maximum caused dramatic shifts in vegetation, which would have disproportionately affected large herbivores and their predators. Therefore, the evidence better supports climate change as the primary cause of megafaunal extinction.