Shaping the human face: Periosteal bone modeling across ontogeny.

Abstract

Facial morphology is a defining aspect of Homo sapiens that distinguishes our species from fossil ancestors and plays a central role in estimating age, sex, and ancestry in both past and present populations. Understanding how the face develops during postnatal ontogeny is essential for interpreting adult facial variation. Periosteal bone modeling (i.e., patterns of resorption and formation) provides direct evidence of bone growth activity underlying morphological variation. This study quantifies periosteal bone modeling in a cross-sectional ontogenetic sample of individuals ranging from birth to adulthood from three geographical populations: Western Europe, Greenland, and South Africa. Epoxy replicas were analyzed using digital microscopy to quantify bone resorption, and digital maps of the bone modeling patterns were created for each facial region-brow ridge, zygomatic, maxilla, and mandible-and projected onto three-dimensional surface models. In parallel, geometric morphometric and multivariate statistical analyses were used to evaluate ontogenetic patterns. Results highlight a consistent sequence of resorption and deposition during human ontogeny and a strong pattern of covariation between bone modeling and shape for most facial regions. The face is largely resorptive from early ontogeny, with deposition increasing with age; the maxilla is significantly more resorptive than other facial regions. Greater resorption in the midface corresponds to significant facial growth and development in early ontogeny, and a developmental shift around adolescence marks the transition from primarily downward to more forward-oriented growth. Overall, the combined approach underscores the developmental coordination of the face and suggests that the human facial growth pattern reflects the need to maintain a non-projecting face from birth on.