Genes, brains and lateralisation: how solid is the evidence?

If there were a dictionary of famous neurological quotes, “On parle avec l'hemisphere gauche” by Paul Broca (1865) would be up there among the top hits. Broca’s realisation that the two sides of the brain are functionally distinct was a landmark observation. It was based on a rather small series of patients, but has since been confirmed in numerous studies. After localised brain injury, aphasia (language impairment) is far more likely after damage to the left side than the right side. […]