Humans differ from their nearest relatives, the chimpanzees and bonobos, in being predominantly right-handed. In the human brain handedness is also associated with an asymmetry in the arcuate fasciculus, favouring the left. This links the inferior parietal, superior and middle temporal cortex with area in the inferior caudal PF cortex (areas 44 and 45B), as well as the ventral PF cortex more anteriorly. There is activation in the inferior caudal PF cortex when subjects imitate, whether via gestures or speech; and damage to the arcuate fasciculus impairs the ability to repeat words. The ability to imitate gestures and sounds was essential for the evolution of learned communication. The left inferior caudal PF cortex (area 44) supports the sequences of speech, whether words, phrases, or sentences. The areas that are connected by the left arcuate fasciculus also support the semantic system. The ability to teach in sentences means that knowledge and skills can be passed on with high fidelity from one generation to another. It also aids communication on cooperative enterprises. The need to cooperate has also led to pressure to be able to understand the intentions of others, and the medial PF cortex forms part of the system that makes this possible. Cooperation requires that individuals obey social and moral rules, and damage to the medial and polar PF cortex impairs the ability to do this.