Walking separately, together, or in mixed groups: Energetic modeling of hominin group locomotion using the Engare Sero archaeological footprint assemblage

Locomotor coordination is a fundamental pillar of human sociality, yet reconstructing group dynamics in deep time remains a significant challenge. The Late Pleistocene footprint site of Engare Sero (Tanzania) provides a unique record of anatomically modern humans moving collectively across a volcanic landscape. While previous studies have inferred group composition and speed from footprint morphology, the energetic implications of these movement patterns have remained unexplored. This study models the Cost of Transport (CoT) and energetic penalties for three representative profiles: adult male, adult female, and non-adult, using experimentally validated quadratic equations. Multiple walking scenarios derived from the Engare Sero assemblage were evaluated, including age-sex-specific means, directional mean speeds (northeast [NE] and southwest [SW]), and the total group average, which were compared with the calculated Optimal Locomotion Speed (OLS) for each profile. The results identify an energetically efficient range between 1.35 and 1.41 m·s⁻¹ (4.86–5.08 km·h⁻¹), where individual optima overlap. The reconstructed group mean speed (1.41 m·s⁻¹) yielded the mathematically lowest overall penalty (0.26%). However, given the female-biased demography of the site (77% adult females), the SW scenario (1.35 m·s⁻¹) appears demographically favorable, reducing the energetic penalty for the majority group to 0.09%. These findings support the interpretation of cooperative mobility in the Late Pleistocene and suggest that prehistoric human locomotion balanced metabolic efficiency with group cohesion.