Assessing the relative length of the metacarpal and metatarsal bones of prehistoric Jomon, Yayoi, and modern Japanese.

Prior studies have reported that Jomon populations exhibit relatively longer distal limb segments (radius and tibia) than their proximal counterparts (humerus and femur) from the Yayoi period onward. However, it remains unclear whether similar intergroup differences exist in the relative lengths of more distal elements, such as metacarpals and metatarsals. This study examined 256 individuals representing the Jomon, Yayoi, and modern Japanese populations, comparing the relative lengths of metacarpals against the humerus and radius, as well as metatarsals against the femur and tibia. The results indicated that, compared to the Yayoi and modern Japanese groups, Jomon individuals consistently had longer metacarpals and metatarsals relative to the humerus and femur. In contrast, no consistent intergroup differences were observed in the relative lengths of the metacarpals and metatarsals relative to the radius and tibia. Additionally, regarding the ratio of the radius to the second through fifth metacarpals, females across populations generally exhibited longer metacarpals than males. These findings suggest that the relative lengths of the metacarpals and metatarsals to the proximal limb segments, similar to the proximal-distal limb segment ratios, may reflect the combined effects of climatic background, population history, and sex-specific morphological variation patterns.