The Birth Canal as Cognitive Architecture Filter: A Unified Molding Principle for Skull, Brain, and Mind Across Birthing Lineages

Organs exert mechanical pressure on the objects passing through them, leaving geometric traces on those objects. This paper proposes that the birth canal functions not merely as a size filter but as an active geometric mold — one whose convulsive, oscillatory dynamics have exerted selection pressure on skull morphology, brain geometry, neonatal developmental state, and ultimately cognitive architecture. Applied comparatively across birthing lineages, this principle offers a unified explanation for species-level divergence in brain organisation and cognitive maturity schedules. A morphological founder effect at the origin of viviparity is proposed as the deep ancestral constraint within which all subsequent birthing geometries evolved.