[Evaluation of the sexing methods using the cranial traits in the Japanese population]

Nowadays, various morphological traits are routinely used for sexing the human skulls. The efficacy and reliability of sexing methods based on these traits in the Japanese population have not been systematically investigated. For sexing the skull, the authors established the well-defined criteria for sexing skulls by using the following five morphological traits; (1) the prominence and texture of the supraorbital arc; (2) the sharpness of the supraorbital margin; (3) the relative size of the zygomatic arc and the existence of a depression on it; (4) the size of the mastoid process and the existence of the supramastoid crest; (5) the prominence of the external occipital crest and the external occipital protuberance, and then evaluated their availability by using 313 recent Japanese skulls (205 males and 108 females) with known sex and age-at-death. We found that the supraorbital arc had the best accuracy rate (80.5%) followed by the mastoid process (78.6%). In cases wherein these two morphological traits indicated the same sex, the accuracy rate increased to 96.3%, suggesting that these traits are particularly useful for sexing the skulls of Japanese individuals. In addition, the accuracy rate of most traits for sexing skulls significantly differed between individuals who were aged < 30 years at death and those who were in their 30s at death. Thus, the influence of aging on the morphological traits of the skulls should not be disregarded in Japanese population. Moreover, similar results were obtained when 120 Edo period Japanese skulls (74 males and 46 females) were studied. This indicates that our method is applicable not only to recent samples but also to the archaeological ones.