Sociality predicts orangutan vocal phenotype

Abstract

In humans, individuals’ social setting determines which and how language is acquired. Social seclusion experiments show that sociality also guides vocal development in songbirds and marmoset monkeys, but absence of similar great ape data has been interpreted as support to saltational notions for language origin, even if such laboratorial protocols are unethical with great apes. Here we characterize the repertoire entropy of orangutan individuals and show that in the wild, different degrees of sociality across populations are associated with different ‘vocal personalities’ in the form of distinct regimes of alarm call variants. In high-density populations, individuals are vocally more original and acoustically unpredictable but new call variants are short lived, whereas individuals in low-density populations are more conformative and acoustically consistent but also exhibit more complex call repertoires. Findings provide non-invasive evidence that sociality predicts vocal phenotype in a wild great ape. They prove false hypotheses that discredit great apes as having hardwired vocal development programmes and non-plastic vocal behaviour. Social settings mould vocal output in hominids besides humans.

Population-specific call order in chimpanzee greeting vocal sequences

“…For primates, there is a puzzling contrast between the advanced vocal production learning capacities of humans, and the very limited capacities of non-human primates (hereafter primates, Egnor and Hauser, 2004 ; Fedurek and Slocombe, 2011 ). In primates, vocal repertoires consist of structurally mostly fixed and genetically predetermined call types (reviewed in Fedurek and Slocombe, 2011 ; Fischer and Hammerschmidt, 2020 ), with individuals possessing only limited flexibility and control over the acoustic structure of the call types within the repertoires (e.g., macaques, Sugiura, 1998 ; marmosets, Elowson and Snowdon, 1994 ; Gultekin et al., 2021 ; Snowdon and Elowson, 1999 ; baboons, Fischer et al., 2020 ; gibbons, Geissmann, 2002 , 1986 ; orangutans, Lameira et al., 2022 , and chimpanzees, Crockford et al., 2004 ; Marshall et al., 1999 ; Mitani et al., 1999 , 1992 ; Watson et al., 2015 ; reviewed in Egnor and Hauser, 2004 ; Fischer and Hammerschmidt, 2020 ).…”

Orangutans also want to be “cool” with their words

“…In a new study published in Nature Ecology and Evolution, scientists found that sociality also drives orangutans' vocal expressions [1]. While earlier experiments have shown such effects in songbirds and marmoset monkeys, this study provides new insights into the "vocal personality" of humans' closest "relatives" -the great apes.…”

Arboreal origin of consonants and thus, ultimately, speech

“…Concurrently, invention and imitation of consonant-like calls by all great apes (from humans and other apes) in captivity [2][3][4], whose lives are mostly terrestrial, suggests that consonant-like call adoption could have been prompted during development, through learning and practice. Therefore, the rich interactions between innate, epigenetic, and social factors that underpin child language acquisition may have been already (at least partly) at play in preverbal ancestral hominids [13].…”