The extinction of large terrestrial mammals, often called megafauna, during the Late Pleistocene 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 correlates strongly with human arrival on different continents. In North America, for example, the disappearance of mammoths, mastodons, and giant ground sloths occurred shortly after the Clovis people crossed the Bering land bridge around 13,000 years ago. Similarly, in Australia, the loss of giant marsupials coincided with the arrival of Aboriginal peoples approximately 45,000 years ago. Second, archaeological evidence reveals that early humans possessed advanced hunting tools, such as the Clovis spear points, which were capable of bringing down large animals. The design of these weapons indicates a specialized ability to hunt megafauna, and kill sites with butchered remains have been discovered at several locations. Third, megafauna were particularly vulnerable to human predation due to their slow reproductive rates. Species such as woolly mammoths had long gestation periods and produced few offspring, making it difficult for their populations to recover from hunting pressure. This combination of human arrival, hunting capability, and biological vulnerability strongly supports the overhunting hypothesis.
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The reading attributes megafaunal extinctions to human overhunting, but this view is flawed. First, the correlation between human arrival and extinction is not consistent. In Africa and Asia, where humans evolved and coexisted with megafauna for hundreds of thousands of years, extinctions were far less severe. If humans were inherently destructive hunters, we would expect the opposite. Second, the archaeological evidence is overinterpreted. Clovis spear points were likely multipurpose tools used for butchering scavenged carcasses or hunting smaller game. Direct evidence of humans killing megafauna—such as embedded projectile points in bones—is rare and often contested. Moreover, many megafaunal species disappeared before the Clovis culture even appeared. Third, while low reproductive rates made megafauna vulnerable, climate change during the Pleistocene was a more decisive factor. Rapid warming at the end of the last ice age altered habitats, reducing the availability of the open grasslands and steppes that these animals depended on. Fossil pollen and sediment records show dramatic vegetation shifts that preceded extinction events. Interestingly, the surviving megafauna in tropical regions were those adapted to flexible diets, whereas the specialized cold-adapted species went extinct, a pattern that aligns with climate-driven habitat loss rather than human hunting.
📝 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.
