Linguistic law-like compression strategies emerge to maximize coding efficiency in marmoset vocal communication

Human language follows statistical regularities or linguistic laws. For
instance, Zipf’s law of brevity states that the more frequently a word is
used, the shorter it tends to be. All human languages adhere to this word
structure. However, it is unclear whether Zipf’s law emerged de novo in
humans or whether it also exists in the non-linguistic vocal systems of
our primate ancestors. Using a vocal conditioning paradigm, we examined
the capacity of marmoset monkeys to efficiently encode vocalizations. We
observed that marmosets adopted vocal compression strategies at three
levels: (i) increasing call rate, (ii) decreasing call duration, and (iii)
increasing the proportion of short calls. Our results demonstrate that
marmosets, when able to freely choose what to vocalize, exhibit vocal
statistical regularities consistent with Zipf's law of brevity that
go beyond their context-specific natural vocal behavior. This suggests
that linguistic laws emerged in non-linguistic vocal systems in the
primate lineage.