TOEFL統合ライティング

📖 読解文章

The discovery of ancient human remains in the Arctic region of Siberia, dating back approximately 30,000 years, has prompted a controversial hypothesis: that early humans migrated to the Americas via a northern route across the Bering Land Bridge much earlier than previously thought. Proponents of this ‘early entry’ theory argue that these Siberian sites, such as the Yana Rhinoceros Horn Site, contain stone tools and animal bones that show human occupation during the Last Glacial Maximum, when ice sheets covered much of North America. They propose three main lines of evidence. First, the presence of distinctive bifacial spear points at these sites resembles Clovis points found in North America, suggesting a cultural link and an early migration. Second, genetic studies of modern Native Americans show a deep divergence time from Asian populations, around 25,000 years ago, which aligns with an early entry. Third, they argue that a coastal route along the Pacific, which would have been ice-free during the Last Glacial Maximum, could have allowed humans to travel southward along the shoreline, bypassing the inland ice sheets. This coastal migration theory is supported by the discovery of marine resources and shell middens at some early sites along the Pacific coast of North America, which suggest a maritime adaptation that could have facilitated rapid southward movement.

🎧 リスニング講義

The lecture challenges each of these points. First, the resemblance between Siberian and Clovis points is superficial. The Yana points are large, leaf-shaped, and lack the characteristic fluting of Clovis points. Moreover, the dating of Clovis sites is firmly around 13,000 years ago, and there is no reliable evidence of Clovis-like technology in Siberia before that time. The similarity could be a result of convergent evolution, not cultural diffusion. Second, the genetic evidence is misinterpreted. The divergence time of 25,000 years may reflect a period when Asian and Native American populations shared a common ancestor in Asia, but this does not mean they entered the Americas then. In fact, more recent genetic studies show that Native American populations diverged from East Asians only about 15,000 to 16,000 years ago, which is consistent with a later entry via an ice-free corridor after the Last Glacial Maximum. Third, the coastal route hypothesis faces a major obstacle: during the Last Glacial Maximum, the Pacific coastline was not ice-free. The Cordilleran Ice Sheet extended to the continental shelf, covering what would have been the coastal plain with ice. Thus, a maritime route would have been impassable until the ice retreated around 17,000 years ago. Even the few coastal sites cited are not older than 14,000 years, which does not support an early entry. Therefore, the evidence does not support a pre-Clovis human presence in the Americas.