This paper investigates the linguistic links between gesture and language, relying on data from signed languages. Data focuses on the developmental routes by which non-linguistic gestures become incorporated into the linguistic system of signed languages. Evidence is presented for two routes: one leading from gesture to word to grammatical morpheme, and a second leading from gesture to prosody to grammatical marker. These two routes emerge because of the semiotic characteristics of hands and faces. One application of this work is to inform research on non-human primate gesture. The goal is to pose new questions about the relation between gesture and language and to propose a new approach that primate gesture researchers may address when surveying the range of gestural forms.