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, population declines began before significant human expansion into mammoth habitats. Fossil records from Siberia show a steady decrease in mammoth numbers starting 20,000 years ago, while human populations in the region remained sparse until 12,000 years ago. Second, mammoths were adapted to cold, dry steppe environments, but the warming climate at the end of the Pleistocene transformed these grasslands into wet, forested tundra. This vegetation shift reduced their primary food sources, leading to malnutrition and reduced reproductive rates. Third, genetic studies of ancient mammoth remains reveal a loss of genetic diversity as climate warmed, with evidence of inbreeding and reduced fertility. These genetic bottlenecks align with periods of rapid temperature increase, not with human hunting pressure. Therefore, climate change, not human activity, caused the mammoths’ demise.

🎧 การบรรยาย

The reading’s argument that climate change alone drove mammoth extinction is flawed. First, the claimed population decline before human expansion is based on incomplete fossil records. Many mammoth fossils from earlier periods have not been preserved due to acidic soils, and new findings in Arctic islands show that mammoths thrived until human hunters arrived there around 4,000 years ago. Second, while climate did alter vegetation, mammoths were not strictly dependent on steppe grasses. Isotopic analyses of mammoth bones indicate they consumed a variety of plants, including sedges and shrubs that expanded with warming. Even in warmer periods, mammoths survived in refugia where food remained abundant. Third, the genetic diversity loss cited by the reading can be linked to human hunting, which fragmented populations and reduced gene flow. In contrast, during earlier warm intervals, such as the Eemian interglacial, mammoths maintained high genetic diversity despite similar climate shifts. Thus, human overhunting, not climate, was the decisive factor.