The origin of meaning in animal signals

Over 40 years ago, Peter Marler proposed that animal signals were adaptive because they provided listeners with information (Marler, 1961, Journal of Theoretical Biology, 1, 295-317). But what was the nature of this information? How did it influence behaviour? And how might the information in animal signals compare with the information in human language? Here we review evidence that signals in a variety of social contexts are adaptive because they convey information. For recipients, meaning results from the integration of information from the signal and the social context. As a result, communication in animals - particularly in long-lived, social species where the same individuals interact repeatedly - constitutes a rich system of pragmatic inference in which the meaning of a communicative event depends on perception, memory and social knowledge. In the human lineage, pragmatics served as a precursor to the later evolution of semantics and syntax. Among primates, there is a striking difference in flexibility between constrained call production and more flexible perception and cognition. However, call production is more flexible in the wild, where it is affected by contextual cues, than in laboratory studies where contextual cues have been removed. Monkeys and apes may overcome the limits of constrained vocal production by producing composite signals in the same and different modalities.