First in, last out?: The evolution of aphasic lexical speech automatisms to agrammatism and the evolution of human communication

Current work in the evolution of language and communication is emphasising a close relationship between the evolution of speech, language and gestural action. This paper briefly explores some evolutionary implications of a range of closely related impairments of speech, language and gesture arising from left frontal brain lesions. I discuss aphasic lexical speech automatisms (LSAs) and their resolution with some recovery into agrammatism with apraxia of speech, an impairment of speech planning and programming. I focus attention on the most common forms of LSAs, expletives and the pronoun+modal/aux subtype, and propose that further research into these phenomena can contribute to the debate. I briefly discuss recent studies of progressively degenerating neurological conditions resulting in progressive patterns of cognitive impairments that promises to provide insight into the evolutionary relationships between speech, language and gesture.