Early hominin morphology at 7–6 Ma shows a coordinated suite of cranial, dental, and postcranial traits that no single locomotor model fully explains. We propose the USO Rooting Adaptation as a complementary framework linking Late Miocene aridification, hydration constraint, risk-sensitive foraging, and sustained skeletal loading. In increasingly seasonal environments, underground storage organs may have provided early hominins with a buffered source of intrinsic moisture and soluble carbohydrates, thereby reducing dependence on spatially restricted, predator-associated water sources. This framework differs from most early hominin foraging models by treating hydration as the first constraint to be solved rather than presuming hydration and moving directly to caloric acquisition. In this view, the initial selective value of underground storage organ use lay in extractive hydration and limited buffering through soluble carbohydrates, whereas more complete caloric exploitation is interpreted as a later development. Repeated extraction and prolonged oral processing of underground storage organs are proposed as potential sources of directionally patterned loading across craniofacial, dental, manual, proximal femoral, distal hindlimb, and possibly vestibular systems. Existing fossil evidence is compatible with some of these expectations, but does not yet distinguish extractive from locomotor loading regimes. The USO Rooting Adaptation is therefore presented not as a replacement for locomotor hypotheses, but as a testable ecological-behavioral framework for evaluating how ecological stress, behavioral adjustment, and extractive foraging may have contributed to early hominin anatomical integration.
Richard DiPasquale (Sat,) studied this question.