# Twice times two: Dual mechanism for double rhythmic meter in orangutans and the evolution of human song

## TL;DR

Orangutans use two different methods to create rhythmic patterns in their calls, offering clues about the evolution of human music.

## Contribution

Discovery of dual mechanisms for double-meter rhythm in non-singing great apes.

## Key findings

- Orangutan long calls show isochrony and double-meter rhythmic patterns.
- Double meter is achieved via tempo shifts and inhale-exhale voicing alternation.
- Human song rhythm may derive from ancestral phonatory-respiratory cycles.

## Abstract

Rhythmic pulse, the division of a beat into subordinate patterns, is the backbone of music. Across the world’s musical traditions, the division of the primary beat into two equal parts – “double meter” – represents a prototypical pulse, also found in singing nonhuman primates. The last great ape common ancestor was, however, a non-singing species. How rhythmic pulse evolved in human song and music is, thus, enigmatic. Here, we analyze wild male orangutan long calls, which are structurally isochronous (i.e., with a steady of 1:1 rhythm). Males divided the primary rhythm into 1:2 and 2:1 subordinate patterns and did so by two distinct mechanisms: tempo changes as used by other primates and voiced in-exhale alternations as still used today by some human song traditions. Findings confirm double-meter in a non-singing great ape and suggest the two-phase cycle of the phonatory-respiratory system may have been leveraged for the evolution of human song and music.

•Orangutan long calls show isochrony and double-meter rhythmic patterns•Double meter achieved via tempo shifts and inhale-exhale voicing alternation•Findings reveal rhythmic pulse in a non-singing great ape species•Human song rhythm may derive from ancestral phonatory-respiratory cycles

Orangutan long calls show isochrony and double-meter rhythmic patterns

Double meter achieved via tempo shifts and inhale-exhale voicing alternation

Findings reveal rhythmic pulse in a non-singing great ape species

Human song rhythm may derive from ancestral phonatory-respiratory cycles

Wildlife behavior; Zoology; Anthropology