The Riverine Hand-Fishing Hypothesis: A Testable Behavioral Model for Coordinated Traits in Human Evolution

Human bipedalism, manual precision, scalp hair, beard growth, eyebrows, reduced body hair, and canine reduction are commonly discussed through partly independent adaptive accounts. This preprint proposes a behavior-first model in which some of these features may have been functionally coordinated within a repeated riverine hand-fishing sequence. The proposed sequence begins with entry into shallow water, visual tracking and manual capture of slippery aquatic prey, progression into deeper water, repeated resurfacing, and exit while carrying food. Four separable experimental programs are specified: wet-grip tests, posture and emergence-load tests, facial-drainage tests, and hair-mediated air-retention tests. The model does not posit a fully aquatic hominin and does not claim that one behavior alone caused all derived human traits. Its scientific value lies in explicit, falsifiable predictions and boundary conditions.