# A bounded hierarchy framework for the evolution of syntax

## TL;DR

This paper proposes a new framework for understanding how human syntax evolved by building on simpler hierarchical structures found in nonhuman animals.

## Contribution

The paper introduces the 'bounded hierarchy' framework as an alternative to existing models for the evolution of human syntax.

## Key findings

- The 'unbounded hierarchy' and 'compositional semantics' frameworks have limitations in explaining the evolution of human syntax.
- Empirical evidence suggests hierarchy exists in nonhuman animals, which supports the 'bounded hierarchy' framework.
- The 'bounded hierarchy' framework traces human syntax origins to simpler hierarchical structures in nonhuman animals.

## Abstract

Is syntax an evolutionary novelty in the human lineage? This question, along with the question of how human syntax evolved, is highly debated in the field of language evolution. In this paper, I reconstruct two prominent frameworks for studying the evolution of human syntax, which I call “unbounded hierarchy” (Bolhuis et al. 2018 in PLoS Biol 16(6):e2005157, 2018. 10.1371/journal.pbio.2005157) and “compositional semantics” (Townsend et al. 2018 in PLoS Biol 16(8):e2006425, 2018. 10.1371/journal.pbio.2006425). I argue that both frameworks face problems when it comes to explaining the evolution of human syntax. Considering these problems, as well as empirical evidence of hierarchy in nonhuman animals, I provide an alternative framework for studying the evolution of human syntax, which I call “bounded hierarchy”. The bounded hierarchy framework that I propose traces the evolutionary origins of human syntax to simpler forms of bounded hierarchy that may be present in extant nonhuman animals.