Handedness, language lateralisation and anatomical asymmetry: relevance of protocadherin XY to hominid speciation and the aetiology of psychosis. Point of view

Within this region of homology a gene — protocadherinXY — has recently been described (Blanco et al, 2000) that is a member of a class of cell adhesion molecules expressed in the brain that have a role in axonal guidance. According to the X—Y theory of cerebral asymmetry, the chromosomal re-arrangements that led to protocadherinX being represented on the Y as well as the X chromosome were speciation events in hominid evolution (Crow, 2000). If the X—Y hypothesis is correct, a component of the variation with respect to this recent and species-specific evolutionary development is epigenetic rather than sequence-based, and it is this, rather than unidentified environmental factors, that accounts for variability of transmission of handedness and psychosis.