The extinction of the woolly mammoth has long been attributed to human overhunting, but recent evidence suggests that climate change was the primary driver. First, the timing of mammoth decline correlates with the end of the last Ice Age (approximately 10,000 years ago), when global temperatures rose rapidly and caused dramatic shifts in vegetation. Mammoths relied on cold, dry steppe-tundra for grazing; as this habitat shrank and was replaced by forests and wetlands, their food supply dwindled, leading to malnutrition and population collapse. Second, archaeological sites show that human hunting of mammoths was sporadic and localized, not intensive enough to cause extinction across continents. For example, in Siberia, where mammoths persisted until 4,000 years ago, human populations were sparse and their hunting tools were primitive. Third, paleontological studies reveal that late-surviving mammoth populations on isolated islands, such as Wrangel Island, exhibited signs of genetic deterioration—reduced genetic diversity and increased birth defects—which are hallmarks of environmental stress rather than hunting pressure. Thus, climate-driven habitat loss, not human activity, was the decisive factor in their demise.
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The professor challenges the reading's claim that climate change was the main cause of mammoth extinction. While climate shifts did occur, they were not unprecedented; mammoths had survived previous interglacial warm periods, such as the Eemian, without going extinct. This suggests that climate alone cannot explain their final disappearance. Regarding the hunting evidence, the reading underestimates human impact. Recent discoveries of mass kill sites, where multiple mammoth carcasses are found with spear points and butchery marks, indicate that humans hunted them effectively and in large numbers, especially in North America. The sparse Siberian populations cited in the reading actually coexisted with humans for a long time, but their extinction coincided with the arrival of more advanced hunting technologies, such as the Clovis points. As for the island populations, the genetic problems observed on Wrangel Island are not evidence of climate stress; rather, they are expected consequences of a small founder population. In fact, these mammoths survived for thousands of years after the mainland populations vanished, and their extinction around 2000 BCE matches the first human arrival on the island, not any significant climate event. Therefore, human predation, both directly and through habitat fragmentation, was the primary 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.
