The Neanderthal cranium: functional reappraisal of a peculiar morphology

Neanderthals (Homo neanderthalensis) display a distinctive craniofacial architecture, with a projecting midface, broad nasal aperture and receding zygomatics, traditionally explained through separate adaptive hypotheses, such as cold adaptation, heavy masticatory loading or specific muscular demands. The cranial base and cervical spine, in turn, have largely been studied in isolation, and a unified account of how these regions functioned together is still lacking. Building on a systematic review of the fossil record (Boggioni et al. 2025), we propose an integrative interpretation in which the neck acts as a structural and functional driver of Neanderthal cranial evolution. From Middle Pleistocene populations such as Atapuerca-Sima de los Huesos to the "classic" Neanderthals of the last glaciation, a suite of cranial and cervical traits covaries as an integrated network shaped by both functional demands and inherited constraints. Short, wide and robust cervical vertebrae with elongated, horizontally oriented spinous processes, an expanded occipital region for powerful nuchal muscles, a reduced external occipital protuberance and a peculiar semicircular canal morphology point to reduced cervical lordosis and limited flexion-extension, favouring head stability over mobility. We argue that this rigidity triggered a "morpho-functional cascade": compensatory changes in head posture and cranial base shape, followed by anterior displacement and reorientation of the mandible with remodelling of the masticatory apparatus, and finally adaptation of the face to forward-shifted dental arcades, resulting in midfacial prognathism. Together with further brain expansion, these changes shaped the definitive Neanderthal morphology. Biomechanically, the occipito-cervical junction worked as a first-class lever balancing nuchal muscles against the facial mass, with the mandible acting as an integrated third-class lever; this coupling limited the need for wide mandibular excursions, preserving airway patency and reducing neurovascular stress. The same configuration may also have served thermoregulation: a short, broad neck reduced exposed surface area, dense musculature contributed to heat production and insulation, and cervical vascular geometry may have limited heat loss. We further hypothesize a role for brown adipose tissue (BAT) in UCP1-mediated non-shivering thermogenesis. The early appearance of many of these traits in European Middle Pleistocene populations, around 400 ka or earlier, is consistent with the accretion model, with repeated glacial cycles amplifying the trend. A strong, stable head-neck system would have favoured short-range, high-intensity activities such as close-contact hunting, in contrast with the lighter, more flexible build of Homo sapiens, better suited to endurance and mobility. Overall, Neanderthal anatomy emerges as a coherent adaptive design in which posture, strength, respiration and thermal efficiency operated as interdependent components, and in which structural constraints actively channelled evolutionary change.