This paper amplifies and develops the motor theory of language origin and evolution presented in previous papers for meetings of the Language Origins Society at Cracow and Oxford in 1985 and 1986. Language is taken to be the capacity of one individual to alter, through structured sound emission, the mental organisation of another individual. In considering the origin of language, we should not look for a distinct, datable origin any more than we would look for a distinct, datable origin for the eye. Language is more than speech just as perception is more than the structure and functioning of the eye. In both cases we have also to be concerned with the neural organisation underlying the functions of speech and visual perception. The fundamental idea is that language was constructed on the basis of a previously existing complex system, the neural motor system. The programs and procedures which evolved for the construction and execution of simple and sequential motor movements formed the basis of the programs and procedures going to form language. At every level of language, from the elementary speech sounds, through the word-forms on to the syntactic rules and structures, language was isomorphic with the neural systems which already existed for the control of movement.