The extinction of large Pleistocene mammals, such as woolly mammoths, saber-toothed cats, and giant ground sloths, has long puzzled scientists. While climate change and human hunting are often cited, a less considered factor is the role of ancient diseases. This essay argues that hyperdisease—a scenario where a pathogen spreads rapidly through populations with no prior immunity—was the primary driver of these extinctions. Three lines of evidence support this claim. First, the timing of extinctions often correlates with the arrival of humans, who may have introduced novel pathogens via domesticated animals or their own bodies. For example, in North America, megafauna disappeared shortly after the Clovis people appeared, suggesting a disease outbreak. Second, the selective nature of the extinctions—many large mammals died out while smaller species survived—is consistent with disease, as pathogens often target specific host species with similar physiological traits. Third, fossil evidence shows that some megafauna populations were in decline before the most severe climate shifts, implying that disease, not climate, initiated their collapse.
🎧 听力讲座
🎯 模拟考试环境：先点「播放讲座」听完内容，再作答。听力原文默认隐藏。
The professor challenges the disease hypothesis. First, while human arrival often coincides with extinction, this does not prove disease. Humans also hunted megafauna, and in many regions, like Australia, extinctions occurred thousands of years before humans arrived—yet disease requires a host to spread, and if no humans were present, how did the pathogen travel? Second, the selective extinction of large mammals actually undermines the disease claim. Diseases typically affect a wide range of species, including small ones, yet small mammals like rodents thrived. Moreover, large mammals have diverse immune systems, so a single pathogen would not likely wipe out all of them. Third, the fossil evidence cited is misleading. Population declines before climate shifts can be explained by other factors, such as habitat loss from gradual warming or competition with other species. In fact, many megafauna survived multiple ice ages, suggesting they were resilient to climate, but they did not survive the arrival of skilled human hunters, who used advanced weapons and drove them to extinction. Thus, human hunting remains a more plausible explanation.
📝 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.
