Spontaneous emergence of language-like and music-like vocalizations from an artificial protolanguage

How did human vocalizations come to acquire meaning in the evolution of our species? Charles Darwin proposed that language and music originated from a common emotional signal system based on the imitation and modification of sounds in nature. This protolanguage is thought to have diverged into two separate systems, with speech prioritizing referential functionality and music prioritizing emotional functionality. However, there has never been an attempt to empirically evaluate the hypothesis that a single communication system can split into two functionally distinct systems that are characterized by music-and languagelike properties. Here, we demonstrate that when referential and emotional functions are introduced into an artificial communication system, that system will diverge into vocalization forms with speech-and music-like properties, respectively. Participants heard novel vocalizations as part of a learning task. Half referred to physical entities and half functioned to communicate emotional states. Participants then reproduced each sound with the defined communicative intention in mind. Each recorded vocalization was used as the input for another participant in a serial reproduction paradigm, and this procedure was iterated to create 15 chains of five participants each. Referential vocalizations were rated as more speech-like, whereas emotional vocalizations were rated as more music-like, and this association was observed cross-culturally. In addition, a stable separation of the acoustic profiles of referential and emotional vocalizations emerged, with some attributes diverging immediately and others diverging gradually across iterations. The findings align with Darwin's hypothesis and provide insight into the roles of biological and cultural evolution in the divergence of language and music.