考古学：ヒトが早くから北米大陸に到達していたことを示す証拠

Humans were living in North America as far back as 30,000 years ago, according to research published in this week’s Nature. Two studies shed light on the much-disputed populating of the Americas, and hint that the continent’s human history goes back further than was previously thought.

The arrival of humans to the Americas marks a major expansion of humans across the planet. The traditional view was that humans first arrived there around 13,000 years ago, and were associated with the Clovis culture (known for its distinctive stone tools). However, the timing and pattern of migration into the Americas remains controversial.

Ciprian Ardelean and colleagues describe the results of excavations at a cave in Zacatecas, central Mexico, including stone tools, plant remains and environmental DNA. Along with dating evidence, their findings suggest that the high-altitude cave was occupied by people between about 30,000 years and 13,000 years ago. In a second study, Lorena Becerra-Valdivia and Thomas Higham used radiocarbon and luminescence ages from 42 archaeological sites in North America and Beringia (a region that historically joined Russia and America) to determine patterns of human dispersal. They produce a statistical model that reveals a robust signal of a pre-Clovis human presence, dating to at least the Last Glacial Maximum (about 26,000–19,000 years ago) and immediately after.

These studies hint that North America was at least thinly populated from a much earlier date than previously suggested—possibly before the Last Glacial Maximum. The findings do not neatly fit with a scenario in which humans first entered North America from Asia via Beringia, before heading south and developing the Clovis culture. The new dates are pre-Clovis, and suggest that humans may have first entered the continent via a route along the Pacific Coast.