Escritura integrada TOEFL

📖 Texto de lectura

The extinction of the woolly mammoth has long been attributed to overhunting by early humans, who migrated across the Bering Land Bridge and spread rapidly through North America and Eurasia. Proponents of this 'overkill hypothesis' argue that mammoths, having evolved in isolation without natural predators like humans, were exceptionally vulnerable to organized hunting. First, archaeological sites such as the Clovis culture in North America show a clear temporal overlap between human arrival and mammoth population decline, with kill sites containing mammoth bones and spear points dated to the same period. Second, mammoths had low reproductive rates—gestation lasted 22 months and females gave birth to a single calf—making their populations slow to recover from even modest hunting pressure. Finally, the rapid warming at the end of the Pleistocene, while often cited as an alternative cause, actually expanded grasslands across the Arctic, which should have favored mammoths rather than harming them. Thus, the most parsimonious explanation for their sudden disappearance is human predation, not climate change.

🎧 Conferencia de audio

The professor challenges the overkill hypothesis, arguing that climate change and other factors better explain mammoth extinction. First, the alleged temporal overlap is misleading. New radiocarbon dating shows that mammoth populations on many Arctic islands, such as Wrangel Island, survived until 4,000 years ago—thousands of years after humans arrived—and only disappeared when sea levels rose and vegetation shrank. This contradicts the idea that human hunting alone caused extinction. Second, the low reproductive rate argument ignores evidence from modern elephants, close relatives of mammoths, which can survive heavy culling if their habitat remains intact. Moreover, mammoth populations in Siberia began declining 20,000 years ago, long before humans reached high densities there, suggesting that hunting was not the primary driver. Third, the reading's claim that warming expanded grasslands is oversimplified. In reality, post-glacial warming led to forest encroachment, peatland formation, and altered seasonal precipitation, which fragmented and reduced the open steppe-tundra habitat that mammoths depended on. Pollen and fossil beetle records show a dramatic loss of grazing habitat just before extinction. Therefore, the lecture concludes that habitat loss due to climate change, not human overhunting, was the decisive factor.