From Muscle to Mind: A Metabolic Allocation Theory of Human Hair Distribution

Human evolution is characterized by cortical expansion, reduced muscular strength relative to other primates, widespread transition from terminal to vellus hair phenotypes, and retention of terminal scalp hair. Existing explanations for human hair distribution have focused on thermoregulation, parasite reduction, aquatic adaptation, endurance locomotion, ultraviolet protection, and sexual selection. While each of these frameworks may contribute explanatory value, none directly addresses the broader metabolic and physiological reorganization that accompanied hominin brain expansion. This manuscript proposes a systems-level metabolic allocation framework suggesting that human evolution involved progressive energetic redistribution away from peripheral muscular force generation and toward centralized neural computation, prolonged cortical development, and fine motor specialization. Within this framework, generalized body hair reduction may represent a downstream consequence of altered metabolic and trophic investment accompanying brain expansion. Drawing on evidence from evolutionary biology, neurodevelopment, mitochondrial function, lactate signaling, and hair follicle biology, the theory proposes mechanistic pathways linking energetic allocation and follicular phenotype. The framework generates multiple testable predictions and is intended as a hypothesis-generating model for future comparative and experimental investigation.