Why is combinatorial communication rare in the natural world, and why is language an exception to this trend?

TL;DR

This paper presents a nonlinear dynamical model explaining the rarity of combinatorial communication in nature, highlighting how cognitive capacities like ostensive communication in humans enable the complex language system.

Contribution

It introduces a new model for the emergence of combinatorial communication and explains why humans are unique in their use of complex language.

Findings

Most combinatorial signals are unlikely to evolve due to interdependence constraints.

Ostensive communication capacity can bypass emergence constraints.

Language's combinatorial complexity is an exception enabled by human cognition.

Abstract

In a combinatorial communication system, some signals consist of the combinations of other signals. Such systems are more efficient than equivalent, non-combinatorial systems, yet despite this they are rare in nature. Why? Previous explanations have focused on the adaptive limits of combinatorial communication, or on its purported cognitive difficulties, but neither of these explains the full distribution of combinatorial communication in the natural world. Here we present a nonlinear dynamical model of the emergence of combinatorial communication that, unlike previous models, considers how initially non-communicative behaviour evolves to take on a communicative function. We derive three basic principles about the emergence of combinatorial communication. We hence show that the interdependence of signals and responses places significant constraints on the historical pathways by which combinatorial signals might emerge, to the extent that anything other than the most simple form of combinatorial communication is extremely unlikely. We also argue that these constraints can be bypassed if individuals have the socio-cognitive capacity to engage in ostensive communication. Humans, but probably no other species, have this ability. This may explain why language, which is massively combinatorial, is such an extreme exception to nature's general trend for non-combinatorial communication.