Hominid Evolution of the Arteriovenous System Through the Cranial Base and Its Relevance for Craniosynostosis

Objective: This paper discusses how the evolving hominid architecture of the arteriovenous system through the cranial base diverted foreseeable pathology in the human brain.

Materials And Methods: Bipedal upright posture was an early adaptation in mosaic morphological pattern changes in hominid evolution; a key feature, the ability of blood to flow either to vertebral or internal jugular venous systems. Encephalization punctuated hominid evolution, its vulnerable feature, a lower threshold for thermal damage. Comparative analysis of ape and human skulls show "fingerprint" structures, revealing big changes in pattern complexity of the cranial vascular tree. Clues to structural/functional changes span data for apes, humans, and hominid fossils. Here, the increasing vascular network, Australopithecus to Homo sapiens, necessitated changes in the blood flow patterns. The transverse-sigmoid (T/S) and occipital-marginal (O/M) venous networks accommodated hydrostatic changes of blood flow, regulating temperature uniquely: the O/M system enlarged, allowing blood to flow straight down into the vertebral plexus without cooling, and added a vast network of emissary/diploic veins, acting as a brain cooling "radiator." This O/M system was fixed in the Australopithecus robustus lineage, p = 0.000001; high frequencies of emissary foramen were selected for over time. Ontologically, the human neonatal O/M system is fully developed; emissary/diploic veins are established by age 5, setting conditions for selective brain cooling.

Conclusion: The Radiator Theory is the evolution of the functionally efficient brain cooling system, fixed in the A. robustus lineage, tying hydrostatic consequences of bipedalism with release of a "thermal constraint" on the encephalizing brain, and reflected in our own ontogeny.