The extinction of the woolly mammoth has long been attributed to human hunting, but recent evidence suggests that climate change was the primary driver. First, the mammoth’s habitat, the mammoth steppe, expanded and contracted with glacial cycles. During the last deglaciation (approximately 15,000–10,000 years ago), warming temperatures caused a rapid shift from dry, grassy steppe to wet, forested tundra, drastically reducing the mammoth’s food supply. Fossil pollen records show that the steppe vegetation declined sharply in this period, coinciding with mammoth population crashes. Second, climate change also affected mammoth reproduction. Warmer, wetter conditions led to increased snow depth in winter, making it harder for pregnant females to find food, thus lowering birth rates. Studies of mammoth remains show a skewed age distribution during this period, with few juveniles, indicating reproductive failure. Third, the timing of extinctions does not match human arrival. In mainland Eurasia, mammoths persisted until about 10,000 years ago, but humans arrived much earlier (around 45,000 years ago). If hunting were the main cause, populations should have declined soon after human arrival, yet they remained stable for millennia. Hence, climate-induced habitat loss and reproductive stress, not overhunting, explain the mammoth’s demise.
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The reading’s argument that climate change alone drove mammoth extinction is flawed. First, while vegetation did shift, mammoths were not strictly dependent on steppe grass. Isotopic analysis of mammoth collagen reveals they consumed a variety of plants, including sedges and forbs, which remained available in warmer periods. Moreover, the mammoth steppe existed during previous interglacials, when temperatures were as warm as the last deglaciation, yet mammoths did not go extinct then. So habitat change alone cannot explain their disappearance. Second, the claim about reproductive failure is speculative. The skewed age distribution cited could result from taphonomic biases, such as selective preservation of adult bones, rather than true low birth rates. Additionally, modern elephants, close relatives, successfully reproduce in snowy environments, suggesting mammoths could adapt. Third, the timing argument actually supports human hunting. In North America, mammoths went extinct about 12,000 years ago, shortly after the Clovis people arrived, and in Eurasia, final extinctions occurred on isolated islands (e.g., Wrangel Island) only after later human colonization. Where humans did not reach until recently, mammoths survived longer. Thus, human hunting, not climate, is the more parsimonious 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.
