Evolutionary dynamics of hyperbolic language

Models of evolution of simple languages have typically assumed full alignment of the speaker and listeners interests, with perfect understanding representing the optimal outcome for both parties. In more realistic settings, communicating individuals will often desire different outcomes from one another. Previous work has shown that misalignment of speaker-listener interests reduces the maximum informativeness among Nash-equilibrium languages, and that multiple equilibrium languages (with different degrees of informativeness) are supported. We study the stochastic evolutionary dynamics of signaling games in which the alignment of speaker-listener interests can vary. We find that increased misalignment of speaker-listener interests is associated with a decrease in information transmission. Moreover, the most common languages to evolve are typically the most informative languages supportable as static Nash equilibria, suggesting a solution to the ‘equilibrium selection problem’. In addition, our dynamics reveal the mechanism by which less informative languages evolve: words that previously signaled intense states come to be used hyperbolically for less intense states, with listeners’ interpretation of these newly-ambiguous words evolving downward in response. We ground our results in linguistic data on intensifiers such as so and very, words which have unique dynamics—with constant recycling and innovation that match our theoretical results well.Author summary: Analyses of signaling and language have typically assumed that both speakers and listeners have a common interest, such as to communicate the location of predators or resources or to convey precise instructions on how to perform a particular task. However, Nature is also rife with situations where mutual interest cannot be assumed. Many such situations have gradated states, signals, and actions, where speaker and listener desire different actions in conjunction with different true states, which are only known to the speaker. For instance, baby birds regularly overstate their true hunger level to their mother, due to a drive to obtain more than the base requirements in attention and nutrients; there are countless parallels in the context of human communication. Previous works in static game theory have established interesting results in modeling misaligned talk, such as the presence of multiple equilibria and the rapid shrinkage of lexica as misalignment of interest increases. Here we expand both the static theory, but also show using evolutionary game theory which equilibria are selected and why. We make a strong connection to linguistics via intensifiers—words such as “so”, “really”, and “very”—which suggests this literature may be immediately salient to sociolinguistics and other disciplines.