Finite-State Syntax in Bengalese Finch Song: Brain, Behavior and Evolution

Abstract

In passerine birds, song is a learned behavior used by males to attract females. Generally, a song is composed of several types of song notes and the order of these notes is stereotyped. However, unlike most songbirds studied to date, Bengalese finches sing non-deterministic songs that may be described by a finite-state syntax. Why do Bengalese finches sing such complex songs? First, to answer from the mechanical point of view, we found that the finite-state syntax is expressed in hierarchically organized brain nuclei in this species. Next, to answer from the functional point of view, we were able to show that a song with syntax is more attractive to female birds, and therefore the song syntax in Bengalese finches may have evolved through sexual selection. Furthermore, to answer from the evolutionary point of view, we found that song syntax was absent in the ancestor species of the Bengalese finch yet females of the ancestor species preferred syntactically complex songs. Based on these results, we discuss the evolution of complex behavior and associated changes in the brain.Through these considerations, we hope to propose a hypothesis on the origin of human language.