Complexity and Simplicity in the evolution of languages across species

Limor Raviv & Cedric Boeckx

In the language sciences, languages with regular and systematic grammars are typically considered to be “simple”, while languages with holistic and idiosyncratic grammars are typically considered to be “complex”. By contrast, in the closely related field of animal communication, these terms are used in exactly the opposite way: communication systems which show regular and systematic structures are considered “complex”, while holistic and idiosyncratic signals are considered “simple”.
Our key message is that this fundamental discrepancy, which has led to conflicting theories and conclusions across adjacent fields, is due to a terminological choice that has created an imaginary tension between what is essentially the same patterns. For instance, population size is reported to have opposite consequences on human vs. animal communication systems: while an increase in human population size is argued to lead to language simplification, an increase in animal population size is argued to lead to signal complexification. We argue that this conflict is only the result of inconsistent use of the same terminology, since in both cases it can be shown that signals become more regular and rule-governed as communities grow.
This unfortunate situation is likely the result of the terms “complex” and “simple” having a loaded social baggage: for some, “simple” is associated with “superior” (e.g., more elegant, optimized), while for others, “simple” is associated with “inferior” (e.g., less sophisticated, unrefined). To make matters worse, terms like “complex” and “simple” are rarely quantitatively or uniformly defined in the relevant literature, and have been used in the past to make potentially harmful and politically-charged judgments on the languages of different communities (e.g., that Creoles are inferior to their ancestor languages; that languages of small, isolated tribes are inferior to those of Western, urbanized communities).
Here, we highlight the problem, its roots, and its implications, and suggest moving away from such biased terms and transitioning to the use of more neutral and descriptive terms (such as compositionality) that can be applied uniformly across fields, leading to parallel descriptions of findings that can be directly compared across species and in turn lead to a more productive dialogue.