The manner and mechanisms by which the human brain has developed its enormous relative size and intricate mode of patterning is one of the most fundamental questions in physical anthropology. Traditionally, the brain was thought to have first enlarged in response to, and concomitantly with, earliest human tool fabrication. It is now known, however, that human tools show up in the fossil record long before brain enlargement, and other theories have subsequently been offered to explain this uniquely human characteristic. This investigator explains brain enlargement as an indirect result of changes in cerebral blood flow and seeks to test two related hypotheses about the pattern of blood flow in hominoids. These hypotheses can be tested by examination of the interior of skulls, because the pattern of meningeal blood vessels provides an indelible imprint on the interior of the skull. The first hypothesis is that the branching pattern of middle meningeal blood vessels distinguishes between the two types of australopithecine fossil. The second is that a "strong" branching pattern correlates with larger cranial capacity. The latter hypothesis will be tested on a large number of human and ape skulls to determine the nature of the correlation between cranial capacity and blood vessel branching pattern in higher primates including humans. The research will provide further evidence regarding the "radiator" theory of brain enlargement, whereby bigger brains are claimed to be characterized by a more complicated network of vessels than smaller brains.
