托福综合写作

📖 阅读文章

The extinction of the megafauna—large animals such as mammoths, giant sloths, and saber-toothed cats—at the end of the Pleistocene epoch has long puzzled scientists. While many factors have been proposed, the most compelling explanation is overhunting by early human hunters. First, archaeological sites across North America and Eurasia show clear evidence of human hunting of megafauna, including spear points embedded in mammoth bones and butchery marks on skeletons. This direct evidence indicates that humans were capable of and did kill these animals in large numbers. Second, the timing of extinctions closely correlates with human arrival. In North America, the Clovis culture appeared around 13,000 years ago, and within a few centuries, most megafauna species vanished. Similarly, in Australia and Madagascar, extinctions followed shortly after human colonization. Third, megafauna species had low reproductive rates—long gestation periods and small litter sizes—making them especially vulnerable to any additional mortality. Even modest hunting pressure could drive populations to decline rapidly, as their birth rates could not compensate for the losses. Therefore, human predation is the primary cause of the megafauna extinction.

🎧 听力讲座

The reading attributes megafauna extinction to human overhunting, but this view is overly simplistic. While there is some evidence of hunting, its scale was likely insufficient to cause extinction. For example, the number of kill sites is remarkably small—only a few dozen across entire continents—whereas if humans had hunted megafauna to extinction, we would expect thousands of such sites. Moreover, the timing correlation is not as clear as claimed. In many regions, megafauna survived for thousands of years after human arrival, and some extinctions occurred during periods of minimal human presence. Climate change provides a stronger explanation. The end of the Pleistocene brought rapid warming and dramatic shifts in vegetation, fragmenting habitats and reducing food sources for large herbivores, which in turn affected predators. For instance, the loss of open grasslands led to the decline of mammoths and horses. Finally, while low reproductive rates made megafauna vulnerable, this vulnerability applies equally to climate stress. When climate altered food availability, these slow-breeding animals could not adapt quickly enough. Thus, the evidence points to climate change, not human hunting, as the dominant cause.