Late Pleistocene evolution of human hairlessness driven by obligate endurance foraging

The evolution of a glabrous, eccrine-dominant integument in Homo sapiens is a singular autapomorphy that fundamentally redefined the hominin thermal niche. While the canonical "Deep-Time Model" (ca. 1.2 Ma) links depilation to persistence hunting, it creates a profound bio-energetic paradox: a hairless physiology millions of years prior to the appearance of cultural buffering. Here, we propose the "Obligate Endurance Foraging (OEF) Hypothesis," arguing that depilation was a rapid Late Pleistocene response (ca. 100–50 ka) to ecological stochasticity and the collapse of high-return niches. We identify the specific selective trigger as a decline in Energy Return on Investment (EROI), which forced a transition to high-mileage foraging radii where metabolic heat dissipation became a hard selective filter. We substantiate this timeline through a functional morphology synthesis, demonstrating a stratigraphic shift from the femoral-dominant "power complex" of archaic humans to the tibia-dominant endurance morphology of modern humans. Crucially, we show that this thermally vulnerable phenotype was only viable through a synchronous "technological compensation package"—specifically water transport (ostrich eggshell flasks) and thermal engineering (tailored clothing, structured hearths). Our synthesis resolves the thermodynamic paradox, positioning hairlessness not as an ancient inevitability, but as a recent "selective scar" of gene-culture co-evolution driven by the metabolic demands of the Late Pleistocene.