Evolution and Development of Brain Asymmetry, and its Relevance to Language, Tool, and Consciousness

Abstract

A brain is said to be asymmetrical or lateralised if one hemisphere is structurally different from the other, or if each hemisphere controls a different set of functions. If the majority of individuals in a population have asymmetries of the same kind and in the same lateral direction, we say that there is hemispheric specialisation. For a long time Western science argued that lateralisation or hemispheric specialisation was a unique characteristic of humans, explaining our "superior" abilities in tool use and language (reviewed by Bradshaw & Rogers, 1992). Indeed, there are still some who essentially adhere to this notion at the present time, seeing cerebral asymmetry as unique to humans at least in its extent, pattern and bias within the population (Corballis, 1991).