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 climate change and human hunting are often cited, a third factor, a hyperdisease, may have been the primary cause. This theory posits that a highly virulent pathogen, carried by domesticated dogs or other commensal animals, swept through populations of large mammals with no prior immunity. Three lines of evidence support this idea. First, the extinction event was remarkably rapid, occurring within a few thousand years across continents, which is more consistent with a fast-spreading disease than with slow climate shifts. Second, many megafauna species that went extinct, such as mammoths and ground sloths, had low reproductive rates, making them especially vulnerable to a disease that could kill a large portion of adults before they could replenish their numbers. Third, the timing of extinctions correlates with the first appearance of dogs in the Americas and Eurasia, suggesting that these animals could have acted as vectors, transmitting the pathogen to wildlife.
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The lecture challenges the hyperdisease hypothesis presented in the reading. While the idea is intriguing, it suffers from several critical flaws. First, the claim that the extinction was uniquely rapid is misleading. In many regions, megafauna disappeared gradually over thousands of years, and some species survived much longer than others. For example, ground sloths persisted in the Caribbean until about 5,000 years ago, long after the proposed disease outbreak. A pandemic would have killed all susceptible species quickly, not leave survivors for millennia. Second, the argument about low reproductive rates is not specific to disease. Species with low reproductive rates are also highly vulnerable to overhunting by humans, and the reading offers no evidence that disease, rather than hunting, was the decisive factor. Indeed, archaeological sites show clear signs of human predation on megafauna, including butchered remains and spear points. Third, the correlation with dog domestication is weak. Dogs were present in many areas long before extinctions occurred, and in some regions, such as Australia, megafauna went extinct before dogs arrived. Moreover, no modern pathogen has been shown to cause such rapid, cross-species mortality in large mammals without also affecting smaller animals, which did not go extinct. Thus, the hyperdisease hypothesis lacks direct evidence and fails to explain the observed patterns.
📝 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.
