Arts1691 Neurolinguistics

Broca (1864) showed that language is located in the left hemisphere (due to an autopsy on an intelligent but language impaired patient after he died). Wernicke (1874) showed that it was also located in a section further back in the left hemisphere.

The younger the brain (less than 5, really) the more flexible it is. Lateralisation isn't as strong when so young, and things can swap sides.

99% of right handed people, and 66% of left handed people have language left-lateralised.
The 33% of left handed people who don't tend to have it spread across both sides, more diffused.

Most complex brain activities require both hemispheres. Even language to an extent – when the right hemisphere is damaged people have difficulty understanding jokes, sarcasm, intonation, etc