Every day we talk about new aspects of the world that surrounds us; aspects that we have never expressed or heard before. Yet, we do not need new words to do so. We use the words we know and combine them in ways that allow us to express these new meanings, and allow  others to understand them. The reason that these new (and potentially very complex) meanings can be understood is because their meaning is predictable from the meaning of their parts and the way these are arranged in sentences. This feature of language is called compositionality, and it is unique to humans and universal to the structure of human communication systems. A much-debated question in linguistics is, how did such compositional structure evolve?

Evolutionary linguists have effectively studied it as (partly) a product of cultural evolution. Languages are culturally transmitted through cycles of learning and communicative interaction. These two dynamics impose pressures that shape the evolution of linguistic structure: a pressure for learnability (for ease of acquisition) and a pressure for expressivity (for effective communication). Compositional structure allows language to be both expressive and learnable, making it possible for users to communicate about a potentially open-ended set of meanings by making (potentially) infinite use of finite means.

However, in order for compositional systems to develop through cultural evolution, human learners need to be able to acquire all these features from the available input and transmit them. Humans therefore need complex skills to learn signals from input, to identify the intentionality behind them to convey a meaning, and to map these signals to their intended meaning (which is compositional). We know that compositional structure of the type found in human language is unique in the animal world, but are these capacities all specific to humans and to language as well? How did these evolve?

Exciting new research is now breaking down this complex communication skill set in other species such as songbirds (e.g., Pied babblers and Zebra finches) and monkeys (e.g., Putty-nosed and Campbell’s monkeys), and opening new research paths to address the great mystery behind the nature of human language. The NCCR Evolving language aims to provide the platform to develop it: stay tuned!