Flat feet may have helped Neanderthals stay stable while carrying heavy loads

In all likelihood, the Neanderthals had flat feet. But it was not a defect at all. Instead, it was the consequence of a precise functional strategy to reduce impact stress under heavy loads and maximize stability on mountainous or rough terrain.

This is just one of the findings that emerged from a study—published in the Journal of Human Evolution—that analyzed for the first time the three-dimensional external shape of the entire heel of Neanderthals, comparing it with that of our species, Homo sapiens.

"The human foot is one of the anatomical structures that best demonstrate our complex evolutionary history, and among the bones it is composed of, the heel plays a crucial role: it is the first structure to touch the ground when walking, cushioning the impact and transmitting the forces to push us forward," explains Maria Giovanna Belcastro, professor at the Department of Biological, Geological, and Environmental Sciences of the University of Bologna, who coordinated the study.

"The 3D analysis of the fossil heels of our ancient cousins, the Neanderthals, has therefore allowed us to highlight both an extraordinary biomechanical adaptation to withstand heavy loads and rough terrains, and the impact of modern life and footwear on our feet."

Heels adapted to heavy loads

The researchers analyzed and compared the heels of seven individuals of the Homo neanderthalensis species with those of 64 individuals of Homo sapiens, ranging from hunter-gatherers of the Pleistocene to farmers of the Iron Age, up to a postindustrial urban population preserved in the Documented Human Osteological Collection of the Certosa Cemetery of Bologna. To do this, they applied advanced 3D geometric morphometry techniques to digital models obtained with laser scans and computed tomography.

The results show clear and fascinating differences. First, compared to the heels of modern humans, those of Neanderthals were shorter, wider and taller. But one of the most surprising aspects concerns the posture and stability of the Neanderthal foot.

Geometric analysis indicates that Neanderthals' foot posture habitually showed pronation. In addition, the study highlights a lower lateral longitudinal arch in Neanderthals, which offered greater flexibility and mobility in the central part of the foot. In short, Neanderthals had flat feet and used this posture to maximize stability and reduce impact stress under heavy loads.

"The robustness of the heel reflects the overall body structure of Neanderthals, which is characterized by remarkable muscle and bone mass and an extremely intense level of physical activity," confirms Belcastro. "These physical characteristics indicate an adaptation aimed at promoting a greater load-bearing capacity on the back of the foot and high mobility on uneven ground."

Modern habits leave a skeletal imprint

Looking instead at our species, the researchers observed that the prehistoric hunter-gatherers of Homo sapiens—who traveled long distances barefoot or with soft footwear—showed heels with characteristics of robustness more similar to those of Neanderthals than those of modern postindustrial populations.

The individuals who have lived in the past centuries have heels that are much weaker, due to a sedentary lifestyle and the habitual use of rigid and closed footwear. This is because the use of shoes with rigid soles tends to limit the inversion and eversion movements of the foot, tightening the ankle: a clear sign of skeletal gracilization due to a drastic reduction in natural biomechanical stimuli.

"The morphology of our skeleton is not only the product of a strict genetic program, but also the consequence of physical stimuli and our daily life habits," explains Belcastro. "The results of this study therefore offer a fundamental contribution to better understand how our ancestors moved in their natural environment and open fascinating prospects for dialogue between evolutionary anthropology and clinical orthopedics."