Call combinations in birds and the evolution of compositional syntax

要旨

Syntax is the set of rules for combining words into phrases, providing the basis for the generative power of linguistic expressions.In human language, the principle of compositionality governs how words are combined into a larger unit, the meaning of which depends on both the meanings of the words and the way in which they are combined.This linguistic capability, i.e., compositional syntax, has long been considered a trait unique to human language.Here, we review recent studies on call combinations in a passerine bird, the Japanese tit (Parus minor), that provide the first firm evidence for compositional syntax in a nonhuman animal.While it has been suggested that the findings of these studies fail to provide evidence for compositionality in Japanese tits, this criticism is based on misunderstanding of experimental design, misrepresentation of the importance of word order in human syntax, and necessitating linguistic capabilities beyond those given by the standard definition of compositionality.We argue that research on avian call combinations has provided the first steps in elucidating how compositional expressions could have emerged in animal communication systems.Language is an essential human trait, but understanding its evolution remains a challenge, in large part because none of humans' close evolutionary relatives (i.e., the great apes) possess communication systems approaching the complexity and flexibility of language [1].The communicative power of language depends on multiple co-occurring capabilities, including referentiality, compositionality, syntax, recursivity, and vocal learning [2].Thus, a profitable approach to gain insights into language evolution is to find and use appropriate analogies of these capabilities in other animals for comparative studies [1,2].Over the past three decades, both field and laboratory studies have revealed that several linguistic capabilities, such as vocal learning and referentiality, did evolve in a range of animal taxa, providing insights into possible evolutionary drivers of these faculties of language (in a broad sense) [2].Here, we review recent studies on bird calls demonstrating the first evidence for another key linguistic capability (i.e., 'compositional syntax' [3]) in a nonhuman vocal system [4-6] and discuss recent criticism of the interpretation of these studies.

主題