Saussure argued that the arbitrariness of symbolic signs shows that language draws from a mental capacity separate from speech since, as he believed, symbols appear in other modalities as in writing and sign languages. This mentalist concept had a broad impact which reflects in current hypotheses of the origin of symbolic language. A review of research shows that, contrary to a mentalist concept, non-human primates have the mental resources serving to learn, use, and combine given symbolic signs, but do not develop symbols in the wild. On the other hand, comparative physiology reveals a human-specific ability to control intonation and oral modulations, and evidence shows that this ability links to the development of inherently symbolic signs in speech, contrary to gestural sign languages which develop from non-arbitrary iconic signs.