Over the past century, the cranial structure of Japanese individuals has evolved significantly, resulting in rounder heads, narrower cheekbones, broader upper jaws, and thinner, more prominent noses.

Although variations outside Japan may exist, global trends suggest similar morphological changes are likely happening worldwide. Shiori Usui from the Chiba Prefectural Science Police Research Institute emphasizes that this is a natural progression as lifestyles modernize globally.

Scientists traditionally use measurements from human remains from the 19th and early 20th centuries to establish baseline comparisons for “modern” humans. Usui explains that today’s populations are generally taller and larger due to advancements in health, diet, and environmental factors, which may also provide insights into head shape changes.

To investigate these changes, researchers utilized CT scans to analyze skulls from 34 men and 22 women who died of natural causes between 1900 and 1920, with their remains donated to Kyoto University School of Medicine for research purposes. They also examined 29 men and 27 women who passed away between 2022 and 2024. Autopsy imaging is increasingly common in Japan, contributing to extensive “virtual skeleton collections,” notes Usui.

Using 3D skull images, researchers identified subtle yet consistent shifts over time. Notably, contemporary individuals are becoming more brachycephalic, as the oval-shaped skulls of the early 20th century are being replaced by rounder forms. While earlier hypotheses suggested these trends, CT scans revealed unexpected differences, including changes in cheekbone structure, nose shape, and forehead contour, which has become shorter and slightly concave over time.

Additionally, the mastoid process, located behind the ear, has increased in size and prominence. Usui emphasizes that these changes are too recent to be attributed to genetic evolution; rather, they likely result from lifestyle factors, such as improved childhood nutrition and the consumption of softer foods requiring less chewing.

Interestingly, the disparities between male and female skulls have intensified compared to a century ago, with male skulls exhibiting stronger brow ridges, larger mastoid areas, and more pronounced facial features than female skulls. “This finding was unexpected,” Usui admits. The team assumed that similar lifestyles between genders would diminish physical differences, leading them to anticipate more “androgynous” facial features, yet their analysis revealed increasing sexual dimorphism.

A recent 2024 US survey indicates that both men’s and women’s facial structures evolve similarly over time. However, a 2000 US study noted a contrasting trend, with head shapes becoming more oval than round, potentially due to earlier studies’ technical limitations, as well as significant changes in the ethnic makeup of the U.S. population due to immigration.

“We aspire to conduct more global research to comprehend how different populations uniquely adapt to rapid environmental modernization,” Usui adds.

Francesco Capello from the University of Palermo highlights that even relatively recent human populations are not fixed; they continue to evolve. “This invites crucial questions regarding the interplay between genetics and environment, especially for traits like bone structure that were once considered stable,” he notes.

The findings underscore the need for scientists to reassess the criteria used for identifying human remains, says Kimberly Plomp from the University of the Philippines Diliman. “The significant changes in modern human skull morphology suggest that existing identification methods may no longer be as reliable as previously thought,” she warns. “This has vital implications for biology and forensic anthropology.”