The evolution of hierarchical structure building capacity for language and music: a bottom-up perspective

Abstract

A central property of human language is its hierarchical structure. Humans can flexibly combine elements to build a hierarchical structure expressing rich semantics. A hierarchical structure is also considered as playing a key role in many other human cognitive domains. In music, auditory-motor events are combined into hierarchical pitch and/or rhythm structure expressing affect. How did such a hierarchical structure building capacity evolve? This paper investigates this question from a bottom-up perspective based on a set of action-related components as a shared basis underlying cognitive capacities of nonhuman primates and humans. Especially, I argue that the evolution of hierarchical structure building capacity for language and music is tractable for comparative evolutionary study once we focus on the gradual elaboration of shared brain architecture: the cortico-basal ganglia-thalamocortical circuits for hierarchical control of goal-directed action and the dorsal pathways for hierarchical internal models. I suggest that this gradual elaboration of the action-related brain architecture in the context of vocal control and tool-making went hand in hand with amplification of working memory, and made the brain ready for hierarchical structure building in language and music.

Keywords: Comparative research; Evolution; Hierarchical structure building; Language; Music; Working memory.

Fig. 1

a Key idea of the current paper. Hierarchical control of goal-directed actions and hierarchical internal models are two central components of hierarchical structure building capacity. The basic brain architecture is shared between nonhuman primates and humans, but has gradually elaborated in the course of the evolution (yellow lines). This elaboration went hand in hand with the elaboration of working memory. Domain-specific representations of language and music emerged as a working memory resource-freeing strategy. b Brain structures central to the current paper. This figure displays the CBGT circuits (green dashed arrows), the dorsal pathways (arcuate fasciculus: orange line; SLF II: light blue line; SLF III: blue line), Broca’s region (BA44 and BA45), and the area Spt (yellow). The brain image was created using a Montreal Neurological Institute (MNI) template provided by MRIcrogl (https://www.mccauslandcenter.sc.edu/mricrogl/). The dorsal pathways were drawn based on Petrides (2014). Abbreviations: area Sylvian parietal-temporal (area Spt); cortico-basal ganglia-thalamocortical circuits (CBGT circuits); superior longitudinal fasciculus (SLF)