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 megafaunal extinctions closely correlates with the arrival of humans on different continents. In North America, for example, the major wave of extinctions occurred around 13,000 years ago, shortly after the Clovis people crossed the Bering land bridge. Second, archaeological evidence supports human predation: kill sites with butchered megafaunal bones and Clovis spear points have been discovered at numerous locations. Third, the selective extinction pattern—favoring large-bodied animals—matches the preferences of human hunters, who would target the largest prey for maximum caloric return. Smaller species, which were less attractive to hunters, largely survived. Thus, overhunting by humans best explains the megafaunal collapse.
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The reading's overhunting hypothesis is appealing but fails to account for several critical lines of evidence. First, timing is not as clear-cut as claimed. In many regions, such as South America and Australia, megafaunal extinctions occurred thousands of years before or after known human arrival, suggesting climate, not humans, as the primary driver. Second, the archaeological record is far more ambiguous. While kill sites exist, they are rare and often show evidence of scavenging rather than active hunting. Moreover, many megafaunal species disappeared without any associated human artifacts. Third, the selectivity pattern actually contradicts hunting pressure. If humans were the cause, we would expect a gradual decline over time as hunting intensified. Instead, the fossil record shows abrupt, simultaneous extinctions across many species—a pattern more consistent with rapid climate change, such as the Younger Dryas cold snap, which altered vegetation and disrupted food chains. Therefore, the evidence points to climate change as the main culprit, not human overhunting.
📝 写作提示 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
