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 many factors have been proposed, the most compelling explanation is overhunting by early humans. First, the timing of extinction correlates strongly with human migration. In North America, megafauna disappeared shortly after the arrival of Clovis hunters, around 13,000 years ago. In Australia, large species vanished soon after human colonization, about 45,000 years ago. Such a consistent pattern across continents suggests a direct causal link. Second, archaeological evidence supports human predation. At multiple sites, researchers have found spear points embedded in mammoth bones and butchery marks on skeletons, indicating that early humans actively hunted these animals. The selective extinction of large, slow-reproducing species is exactly what would be expected if humans preferentially hunted them for meat and hides. Third, climate change alone cannot explain the pattern. The Pleistocene experienced numerous glacial-interglacial cycles, yet megafauna survived earlier warming events. Only when humans arrived did these animals disappear, even during periods of stable climate. Therefore, human overhunting is the primary cause of the megafaunal extinction.
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The professor challenges the overhunting hypothesis presented in the reading. While the timing correlation seems striking, it is not as simple as stated. In many regions, megafauna coexisted with humans for thousands of years before their extinction. For example, in Eurasia, woolly mammoths and humans overlapped for over 30,000 years, and in South America, some large animals survived for millennia after human arrival. This undermines the claim that human migration led to immediate extinction. Furthermore, the archaeological evidence is far from conclusive. The so-called butchery marks on bones may actually be from scavenging, not hunting. Early humans might have used tools to carve meat from animals that died of natural causes or were killed by other predators. Indeed, cut marks on bones do not prove that humans killed the animal. Finally, climate change cannot be dismissed as easily as the reading suggests. The late Pleistocene was marked by rapid and extreme climate fluctuations, including the Younger Dryas cold snap, which drastically altered vegetation and water sources. These environmental stresses could have reduced megafauna populations to critical levels, making them vulnerable to any additional pressure, including human hunting. Thus, the extinction likely resulted from a combination of climate and human factors, not overhunting alone.
📝 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.
