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 human overhunting, known as the 'Pleistocene overkill' hypothesis. First, the timing of extinctions closely matches the arrival of humans on different continents. In North America, for example, the megafauna vanished roughly 13,000 years ago, soon after the Clovis people crossed the Bering land bridge. Second, archaeological evidence shows that early humans actively hunted large animals. Clovis spear points have been found embedded in mammoth skeletons, and kill sites with butchered remains are common. Third, the selective extinction of large-bodied species supports human hunting, because these animals would have provided the most meat per kill and were more vulnerable due to their slow reproduction rates. Smaller species, which were less attractive to hunters, survived. These lines of evidence collectively argue that human predation was the primary driver of the megafaunal extinctions.
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The reading's claim that human overhunting caused the megafaunal extinctions is not convincing. While the timing of human arrival and extinctions overlaps, correlation does not imply causation. In many regions, megafauna disappeared thousands of years before humans arrived, as in Australia where extinctions occurred 50,000 years ago, but human presence dates back 70,000 years—a gap that weakens the overkill scenario. Furthermore, the archaeological evidence is far too sparse. Only a handful of Clovis kill sites exist, and many are contested. For every mammoth with a spear point, there are dozens of extinct species with no evidence of hunting at all. If humans were the sole cause, we would expect widespread kill sites across species, not just a few large animals. Finally, the selectivity argument ignores climate change. The end of the Pleistocene saw dramatic warming and shifts in vegetation, which fragmented habitats. Large animals, which require vast territories and abundant food, would have been more severely affected than small ones. Indeed, many megafauna species had already survived earlier human hunting pressures, but they could not cope with rapid environmental change. Thus, climate change, not human overkill, better explains the pattern.
📝 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.
