Viết tích hợp TOEFL

📖 Đoạn văn

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 timeline of mammoth decline correlates more closely with warming temperatures than with human migration. Radiocarbon dating shows that mammoth populations began to shrink dramatically around 15,000 years ago, a period of rapid warming, whereas humans arrived in Siberia much earlier, around 30,000 years ago, without causing significant decline. Second, habitat loss due to rising sea levels and vegetation shifts would have been catastrophic. As the Ice Age ended, grasslands—the mammoths’ primary food source—were replaced by forests and tundra, reducing their grazing range. Fossil pollen records indicate that these vegetation changes occurred precisely when mammoth numbers fell. Third, the genetic diversity of late mammoths was already low, indicating a population under stress from environmental factors, not from hunting pressure. Studies of mitochondrial DNA from mammoth remains show a steady loss of genetic variation over the last 50,000 years, consistent with a shrinking habitat, whereas hunting typically causes rapid, localized extirpation rather than a gradual genetic decline. Thus, while humans may have delivered the final blow, climate-driven ecological change was the fundamental cause.

🎧 Bài giảng

The reading’s argument that climate change drove mammoth extinction is unconvincing. First, the correlation between warming and decline is misleading. Human hunting pressure was not constant; it intensified with better weapons and social organization. In fact, the most rapid mammoth decline occurred after 12,000 years ago, exactly when human populations expanded and developed sophisticated hunting techniques, such as using spears and driving herds off cliffs. Second, the vegetation shift argument ignores that mammoths were adaptable. Fossilized dung and teeth show that they consumed a varied diet, including shrubs and herbs, not just grasses. Moreover, similar warming periods occurred earlier in the Pleistocene, yet mammoths survived those changes. The only unique factor in the late Pleistocene was the presence of advanced human hunters. Third, low genetic diversity does not imply climate stress. Small, isolated populations can lose diversity due to random genetic drift, and human hunting could have fragmented populations, leading to inbreeding. In fact, genetic data from Wrangel Island, where mammoths survived until 4,000 years ago, show that a small population persisted for thousands of years despite low diversity, indicating that genetic decline alone was not fatal. Therefore, the evidence better supports human overhunting as the primary cause.