Skulls of Japanese people have grown rounder with wider jaws and other changes in the past 100 years, according to a new study. Researchers attribute the shifts to improvements in health, diet, and environment rather than genetics. The findings challenge traditional references for modern human anatomy.
Scientists at Japan's National Research Institute of Police Science analyzed CT scans of skulls from people who died between 1900 and 1920, as well as those from 2022 to 2024. The study, published in the American Journal of Biological Anthropology, measured 161 landmarks on 3D images and found consistent changes. Heads have become more brachycephalic, shifting from oval to rounder shapes, with narrower cheekbones, wider upper jaws, slimmer noses, shorter foreheads, and larger mastoid processes behind the ears, said lead researcher Shiori Usui. Usui noted that these alterations are too rapid for genetic evolution and likely stem from better childhood nutrition, softer foods requiring less chewing, and overall healthier lifestyles. Surprisingly, differences between male and female skulls have increased, with men showing stronger brow ridges and more projecting faces. “This was a striking and unexpected result for us,” Usui said, adding that the team had anticipated fewer distinctions due to converging lifestyles. While focused on Japan, Usui suggested similar trends occur globally amid modernization. A 2024 US study hinted at comparable facial changes, though a 2000 study reported more oval shapes, possibly due to methodological limits or immigration effects. Experts like Francesco Cappello of the University of Palermo emphasized ongoing environmental influences on bone morphology. Kimberly Plomp of the University of the Philippines Diliman warned that such rapid changes could outdated forensic identification methods. “If modern human crania... have significantly changed in morphology in such a short period of time, this could mean that the methods we use are no longer as accurate as hoped,” she said.