The extinction of large terrestrial mammals, such as woolly mammoths and saber-toothed cats, at the end of the Pleistocene epoch has long puzzled scientists. While climate change and human hunting are often cited, a less discussed but compelling theory points to a hyperdisease caused by a novel pathogen. This theory suggests that a highly contagious and lethal microorganism, inadvertently introduced by early humans or their domesticated animals, swept through susceptible megafauna populations, causing rapid decline. Three key pieces of evidence support this hypothesis. First, the timing of extinctions correlates with human migration patterns, not just climate shifts. In North America, megafauna disappeared around 13,000 years ago, coinciding with the arrival of Clovis hunters, whereas in Eurasia, extinctions were staggered, matching later human expansions. Second, the selectivity of the extinctions—favoring large-bodied species with low reproductive rates—is consistent with a disease that disproportionately affects species with small population sizes and slow recovery, as these are more vulnerable to epidemic-driven crashes. Third, the suddenness of the disappearances, often within a few thousand years, argues against a gradual climate driver, which would likely cause more staggered declines. Instead, a swift pandemic could explain the near-simultaneous demise of diverse species across continents.
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The hyperdisease theory, while intriguing, faces serious challenges that undermine its credibility. First, the correlation between human arrival and extinction is not as clean as proponents claim. In many regions, such as Australia, megafauna extinctions occurred tens of thousands of years before humans arrived, and in others, like parts of Africa, large mammals survived despite long human coexistence. Moreover, the timing in North America is debated; some extinctions predate Clovis, and others persist for millennia after, suggesting a more complex pattern than a single epidemic. Second, the selectivity argument actually supports climate and hunting hypotheses better. Large-bodied, slow-reproducing species are also more vulnerable to habitat loss and hunting pressure, as they require vast territories and produce few offspring. For instance, during historical climate shifts, such as the Younger Dryas, vegetation changes would have disproportionately affected these giants, reducing their food sources. Third, the suddenness of extinction is not unique to disease; rapid climate events, like the abrupt cooling at 13,000 years ago, can cause swift ecological disruption. Furthermore, no direct evidence—such as ancient pathogen DNA in fossil bones—has been found, despite extensive searches. Without such proof, the hyperdisease theory remains speculative and fails to account for the observed geographic and temporal variations.
📝 คำแนะนำการเขียน Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
📊 TOEFL Integrated Writing Rubric
Content Accuracy: Accurately capture the relationship between lecture and reading
Information Completeness: Cover all key counter-arguments from the lecture
Structure & Coherence: Logical organization and progression
Language Use: Grammar, vocabulary, expression accuracy
Scored 0-30 based on holistic scoring (original 0-5, scaled to 30).
