Abstract
Prehistoric Jomon hunter-gatherers are distinct from majority of the Iron Age Yayoi and later populations of Japan in showing distally elongated intra-limb proportion. Intra-limb proportion in modern humans is often linked to ecogeographic rule of Allen, and is considered to reflect local temperature. If this is correct, considerably large intra-limb proportion of Jomon suggests their adaptation to tropical climate, and contradicts with the fact that they had lived on the temperate/subarctic Japanese archipelago for more than 10000 years. However, the original Allen’s rule denotes size proportion between trunk and appendages, and this proportion better associates with climate in humans rather than intra-limb proportion. In this study, we investigate relative limb lengths compared to trunk size in Jomon, “immigrant” Yayoi, and early-modern Edo populations of Japan. The ratios of Jomon and Yayoi are similar to each other, and are comparable to those for temperate/subarctic populations of Europe. Therefore, the body shape of Jomon is not a tropical type in view of thermoregulation. This finding does not exclusively support but is at least consistent with the recent hypothesis that Jomon originated from a Paleolithic population inhabited in Northeast Asia. However, the low ratios found in the sample of short-statured Edo people suggest that intra-limb proportion is sometimes affected by environmental factors other than climate. On the other hand, principal component analyses based on bi-iliac breadth and limb bone lengths indicate significant differences in overall body form between Jomon and Yayoi, particularly in males. Such differences probably reflect different genealogical backgrounds of these two populations.
