Distinctively human: cerebral lateralisation and language in Homo sapiens

Th ree lines of evidence: handedness, brain anatomy and cognition in great apes, extinct hominids and modern humans suggest that cerebral lateralisation underlies the human capacity for language. Chimpanzees do not show consistent population level handedness. Cultural artefacts and post-cranial anatomy allow some investigation of cerebral asymmetry and handedness in extinct hominids suggesting the presence of handedness in early Homo species. Directional handedness on a population basis is present and universal in modern Homo sapiens. In anatomical structure of the brain two components of macroscopic asymmetry are dissociable: i) “petalia”, the protrusion of the right frontal and left posterior poles relative to their counterparts in the opposite hemisphere, seems to have an older evolutionary origin and be unrelated to language, ii) a “volume asymmetry” that may be Homo sapiens-specifi c and associated with the microscopic asymmetry of cell organisation in human language cortex that is not found in other apes. Sex diff erences in structural and functional asymmetry which are plausibly related to sex diff erences in verbal ability are found in human populations without established counterparts in chimpanzees and indicate a possible role of sexual selection in human lateralisation. Th e mapping of major elements from historical language models onto the asymmetric human brain is illustrated. Th e microscopic asymmetry of cell and minicolumn spacing is suggested as a neural basis for recursive processing.