“The human foot is one of the most complex masterpieces of evolution, a work of art in biomechanics: not only it allows us to walk, run and jump, but it is also a true witness of our past and our present,” said Rita Sorrentino, PhD, a researcher at the Department of Biological, Geological and Environmental Sciences at the University of Bologna and first author of an extensive study shedding new light on the complex evolution of human feet.
An international, multidisciplinary team of paleoanthropologists, bioarcheologists, biomechanical engineers, and orthopedists was led by researchers at the University of Bologna to study the medial longitudinal arch of the foot, a unique characteristic that differentiates Homo sapiens from nonhuman primates.
The longitudinal arch is a functional adaptation that allows the foot to switch from a shock absorber function to lever during the phases of contact and detachment with the ground, a mechanism that allows humans to have an efficient bipedal walk. Despite its importance, however, it is still unclear when this characteristic appeared in the course of evolutionary history. The topic of flat feet, a flattening of the medial longitudinal arch, complicates the picture even more.
“Not all flat feet are the same and yet there is not a worldwide clinical definition of flat feet in human beings,” said Alberto Leardini, PhD, and Claudio Belvedere, PhD, scientists from the Rizzoli Orthopaedic Institute and among the authors of the study. Scientists have focused on the role of the navicular bone to find answers, the keystone of the medial longitudinal arch of the foot.
“The results of this research highlight the variation of navicular morphology among flat-footed people and people with a well-developed longitudinal arch,” said Maria Giovanna Belcastro, PhD, University of Bologna. “More specifically, people who developed flat feet during adulthood show differences concerning the navicular bone shape compared to those with regular arches or with inborn flat feet.”.
This development raises questions about the nature of inborn flat feet, suggesting that they may represent a normal variant of foot morphology, and thus highlighting the importance of bone morphology in the structure of the foot arch.
The results suggest that the development of the longitudinal arch may be influenced by factors such as the type of footwear, lifestyle, and prevailing locomotion strategies.
“We have observed that individuals belonging to hunter-gatherer groups, who live without footwear, show feet that are more flexible in mobility and relatively flatter than those of populations using modern footwear,” said Damiano Marchi, PhD, University of Pisa, one of the coordinators of the study. “These differences may come from different cultural lifestyles and practices: the feet of hunter-gatherer populations could therefore represent a form closer to that of our prehistoric ancestors.”
The investigation also compared foot structure with fossils of ancient Homo sapiens and other human species of the past. The research ultimately offers a new perspective on the evolution of the human foot and its variability, contributing to our understanding of how this body part has adapted to bipedal locomotion, the researchers said.
“Our foot is a true witness to our past and our present, a fascinating chapter in the great history of human evolution. The results of this investigation provide a comprehensive overview of the morphological variability of the human foot throughout evolution and raise important questions about congenital flat feet, suggesting that they may represent a normal variant of human foot morphology,” said Sorrentino.
Researchers and professionals from the following universities and institutes took part in the research: University of Pisa, IRCCS Rizzoli Ortophedic Institute, University of Southern California, University of the Witwatersrand, University of Colorado, Monash University, Collège de France-Paris, Max Planck Institute for Evolutionary Anthropology, Georgian National Museum, Institute for Anthropological Research-Zagreb, University of Southern California, Washington University in St. Louis, New York University, Naturalis Biodiversity Center-Leiden, Western University, The Pennsylvania State University, Dartmouth College.
Editor’s note: This story was adapted from materials provided by the University of Bologna.
The open-access study, “Morphological and evolutionary insights into the keystone element of the human foot’s medial longitudinal arch,” was published in Communications Biology.
