Gestures are processed in the same areas of the brain as speech and sign language such as the left inferior frontal gyrus (Broca's area) and the posterior middle temporal gyrus, posterior superior temporal sulcus and superior temporal gyrus (Wernicke's area). It has been suggested that these parts of the brain originally supported the pairing of gesture and meaning and then were adapted in human evolution "for the comparable pairing of sound and meaning as voluntary control over the vocal apparatus was established and spoken language evolved". As a result, it underlies both symbolic gesture and spoken language in the present human brain. Their common neurological basis also supports the idea that symbolic gesture and spoken language are two parts of a single fundamental semiotic system that underlies human discourse.