The extinction of the woolly mammoth (Mammuthus primigenius) at the end of the Pleistocene has long intrigued scientists. While climate change and human hunting are often cited, a less considered factor is the role of infectious disease. Three lines of evidence support this hypothesis. First, ancient DNA analyses of mammoth remains reveal the presence of pathogens, including viruses and bacteria, that could have caused epidemics. For instance, a 2018 study identified sequences similar to modern pathogens in mammoth bone samples, suggesting that these animals were exposed to infectious agents. Second, the timing of extinction aligns with the spread of other species, such as early domestic dogs and humans, which could have introduced novel pathogens to naïve mammoth populations. The lack of immunity would have made them highly susceptible, leading to rapid population declines. Third, the extinction occurred in a relatively short period (a few thousand years), which is more consistent with a disease outbreak than with gradual climate shifts or sustained hunting pressure, which would likely cause a more protracted decline. Therefore, disease, not climate or hunting, was the primary driver of the mammoth's demise.
🎧 听力讲座
The professor challenges the disease hypothesis presented in the reading. First, the presence of pathogen DNA in mammoth fossils does not prove that these pathogens caused death. Many microbes are harmless commensals or post-mortem contaminants. The reading's cited study lacked evidence of active infection, such as lesions or immune responses, so the mere presence of DNA is inconclusive. Second, the proposal that dogs or humans introduced novel pathogens is speculative. There is no direct evidence of a specific pathogen that jumped species and caused a mammoth epidemic. Moreover, if such a deadly disease had emerged, it would likely have affected other large mammals sharing the same habitats, but we see no similar synchronous declines in species like bison or horses. Third, the rapid extinction timeline actually supports the human hunting hypothesis, as newly arrived human hunters with advanced weapons could have overhunted mammoths in just a few thousand years. In contrast, a disease would require efficient transmission and high mortality, but mammoth populations were sparse and widely dispersed, making it difficult for a pathogen to spread rapidly. Thus, the evidence better aligns with hunting pressure, not disease.
📝 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.