การเขียนเชิงบูรณาการ TOEFL

📖 เนื้อเรื่อง

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 timing of mammoth decline correlates closely with the end of the last Ice Age, when global temperatures rose dramatically. As the climate warmed, the vast grasslands known as the mammoth steppe—their primary food source—were replaced by forests and tundra, reducing their habitat and causing population fragmentation. Second, genetic studies of ancient mammoth remains reveal a significant loss of genetic diversity just before extinction, which is more consistent with a slow environmental stress than with sudden human predation. Low genetic diversity would have made them susceptible to disease and reduced their ability to adapt to changing conditions. Third, human hunting, while present, was likely limited in scale. Archaeological sites from the period show that early humans primarily hunted smaller game, such as reindeer and horses, and mammoth bones found at these sites are often from old or sick individuals, suggesting opportunistic scavenging rather than systematic hunting. Therefore, the woolly mammoth’s demise was a consequence of natural climate shifts, not human activity.

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The reading’s argument that climate change alone drove mammoth extinction is unconvincing. While it is true that warming altered habitats, the mammoth steppe did not disappear uniformly—it persisted in refugia such as northern Siberia and Alaska until after the mammoths vanished there. Moreover, the loss of genetic diversity can be explained by human hunting, which reduces populations and isolates groups, leading to inbreeding—this is seen in modern elephants. As for the claim that humans hunted only small game, this ignores evidence from kill sites like Clovis, New Mexico, where mammoth remains are found with spear points and show clear butchering marks on healthy adults. Additionally, human populations expanded precisely when mammoth numbers crashed, and on islands like Wrangel, where humans arrived later, mammoths survived for thousands of years longer than on the mainland. This pattern—extinction following human arrival—is a classic signature of overhunting. Finally, if climate were the sole cause, we would expect a gradual decline across all regions, but instead we see sudden collapses coinciding with human migration waves. Thus, the lecture shows that human activity, not climate, was the decisive factor.