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 mammoth population began to decline approximately 20,000 years ago, well before humans arrived in their primary habitats in Siberia and North America. Fossil records show a steady decrease in numbers during the Last Glacial Maximum, when human hunting pressure was minimal. Second, mammoths were highly specialized grazers, feeding primarily on cold-adapted grasses. As the climate warmed and glaciers retreated, these grasses were replaced by forests and tundra shrubs, reducing the mammoths’ food supply. Isotopic analysis of mammoth bones reveals a shift in diet toward less nutritious plants just before extinction. Third, the warming climate also caused widespread habitat fragmentation. Rising sea levels flooded the Bering Land Bridge, isolating mammoth populations on islands and preventing migration to suitable feeding grounds. Genetic studies of the last surviving mammoths on Wrangel Island show signs of inbreeding and reduced genetic diversity, making them vulnerable to disease and environmental stress. While humans may have delivered the final blow to small, isolated groups, the overarching cause of extinction was climate-induced environmental change.
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The reading argues that climate change drove mammoth extinction, but this view is flawed. First, the claim that human hunting was minimal 20,000 years ago ignores archaeological evidence. Butcher marks on mammoth bones and spear points found at sites in Siberia date to 45,000 years ago, proving humans hunted mammoths long before the decline began. Second, the idea that warming destroyed their food supply is contradicted by the fact that mammoths survived interglacial periods in the past. During previous warm episodes, they adapted by shifting to different vegetation, such as sedges and forbs. The isotopic data the reading cites actually show a dietary shift, but this occurred only after populations were already decimated by hunting, not as a primary cause. Third, habitat fragmentation from rising seas was not a major factor because mammoths were excellent swimmers—they routinely crossed water bodies. The Wrangel Island population, often cited as evidence of climate stress, survived for thousands of years after the mainland extinction, and their genetic issues were due to a small founder population, not climate. In fact, the final extinction of Wrangel mammoths around 4,000 years ago coincides with the arrival of human settlers on the island, not with any major climate shift. Therefore, human overhunting remains the most plausible 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.
