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 appeared. Second, archaeological evidence supports human predation: kill sites with butchered remains of megafauna, such as the Clovis points found embedded in mammoth bones, indicate that these animals were actively hunted. Third, the selectivity of extinction—favoring large-bodied species that reproduce slowly—aligns with the pattern expected from human hunting pressure, as these species would be particularly vulnerable to additional mortality. In contrast, smaller, faster-reproducing animals survived, suggesting that humans did not cause a general environmental collapse but rather targeted the largest prey.
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The lecture challenges the overhunting hypothesis, arguing that climate change was the primary driver of megafaunal extinction. First, the timing argument is flawed: in many regions, such as Eurasia, megafaunal populations began declining thousands of years before humans arrived. For instance, woolly mammoths in Siberia started to dwindle 20,000 years ago, while humans only appeared there 12,000 years ago. This mismatch undermines the idea that hunting was the trigger. Second, the archaeological evidence is weaker than claimed. Kill sites are rare and often ambiguous; many so-called 'butchered' bones may have been scavenged after natural death, not hunted. Moreover, the number of humans at that time was too small to have caused such rapid extinction across vast continents. Third, the selectivity argument actually supports climate change: large animals are more susceptible to heat stress and require more food and water, making them less resilient to rapid environmental shifts. The extinction pattern correlates with periods of abrupt warming and vegetation change, not with human population density. Therefore, the evidence points to climate, not hunting, as the main cause.
📝 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.
