Brain endocast asymmetry in pongids and hominids: Some preliminary findings on the paleontology of cerebral dominance

Abstract

Observations on petalial asymmetry for 190 hominoid endocasts are reported and their statistical differences assessed. While all taxa of hominoids show asymmetries to various degrees, the patterns or combinations of petalial asymmetries are very different, with fossil hominids and modern Homo sapiens showing an identical pattern of left-occipital, right-frontal petalias, which contrasts with those found normally in pongids. Of the pongids [Gorilla gorilla, Pan paniscus, P. troglodytes, Pongo pygmaeus] Gorilla shows the greater degree of asymmetry in left-occipital petalias. Only modern Homo and hominids (Australopithecus, H. erectus and Neanderthals) show a distinct left-occipital, right-frontal petalial pattern. Analysis by .chi.2 statistics shows the differences to be highly significant. Due to small sample size and incompleteness of endocasts, small-brained hominids, i.e., Australopithecus, are problematical. To the degree that gross petalial patterns are correlated with cognitive task specialization, human cognitive patterns probably evolved early in hominid evolution and were related to selection pressures operating on symbolic and spatiovisual integration. These faculties are corroborated in the archaeological record.