Population expansion of early Upper Palaeolithic hunter-gatherers triggered cultural complexity on Paleo-Honshu Island, Japan.

The major expansion of Homo sapiens represented by the Initial Upper Palaeolithic is one of the most significant prehistoric events in Eurasia, potentially leading to the replacement of archaic humans by Homo sapiens or the exploitation of new territories. Recent genetic studies suggest that Initial Upper Palaeolithic hunter-gatherers, or their descendant populations, expanded further east beyond the distribution area of Initial Upper Palaeolithic sites. However, the early Upper Palaeolithic sites, which appeared around 38 ka in Japan, are distinct and exhibit cultural traditions different from the Initial Upper Palaeolithic or other early Upper Palaeolithic assemblages in eastern Eurasia. The origins of the Japanese early Upper Palaeolithic remain unknown, and their formation process has yet to be quantitatively confirmed. In this study, we reconstruct a precise absolute chronology for Japanese early Upper Palaeolithic sites using reliable radiocarbon dating and examine the spatiotemporal patterns of early Upper Palaeolithic components. The results indicate that the number of early Upper Palaeolithic sites expanded between 36 and 34 ka, and the early Upper Palaeolithic assemblages indicate high complexity at this phase. The expansion of the population size between 36-34 ka would have provided hunter-gatherers with the opportunity for creating new tools and technologies and sharing them among different groups, leading to distinctive, complex early Upper Palaeolithic assemblages widespread in Japan.