Orangutan information broadcast via consonant-like and vowel-like calls breaches mathematical models of linguistic evolution - PubMed (original) (raw)

Orangutan information broadcast via consonant-like and vowel-like calls breaches mathematical models of linguistic evolution

Adriano R Lameira et al. Biol Lett. 2021 Sep.

Abstract

The origin of language is one of the most significant evolutionary milestones of life on Earth, but one of the most persevering scientific unknowns. Two decades ago, game theorists and mathematicians predicted that the first words and grammar emerged as a response to transmission errors and information loss in language's precursor system, however, empirical proof is lacking. Here, we assessed information loss in proto-consonants and proto-vowels in human pre-linguistic ancestors as proxied by orangutan consonant-like and vowel-like calls that compose syllable-like combinations. We played back and re-recorded calls at increasing distances across a structurally complex habitat (i.e. adverse to sound transmission). Consonant-like and vowel-like calls degraded acoustically over distance, but no information loss was detected regarding three distinct classes of information (viz. individual ID, context and population ID). Our results refute prevailing mathematical predictions and herald a turning point in language evolution theory and heuristics. Namely, explaining how the vocal-verbal continuum was crossed in the hominid family will benefit from future mathematical and computational models that, in order to enjoy empirical validity and superior explanatory power, will be informed by great ape behaviour and repertoire.

Keywords: great apes; language evolution; language origin; orangutans (Pongo spp.); proto-consonants; proto-vowels.

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Figures

Figure 1.

Figure 1.

Spectrographic representation of orangutan consonant-like and vowel-like calls (a), graphic representation of the experimental set-up (b), and acoustic performance during transmission (c_–_f), (based on raw data). uncal., uncalibrated. Box plots represent median and 25–75% interquartile range; whiskers represent lowest/highest value within 1.5 times interquartile range below/above; outliers omitted for clarity. Linear trend lines represented across distance are for visual aid only (based on raw data). *p < 0.001 (LMM ANOVA; see table 1).

Figure 2.

Figure 2.

Graphical representation of information performance of orangutan consonant-like and vowel-like calls during transmission, as measured by percentage of correctly assigned cases over distance. Black dotted lines: chance level. (a) Continuous lines: correctly classified cases (DFA); dashed lines: correctly classified cross-validated cases (DFA leave-one-out). (b,c) Continuous lines: correctly cross-classified cases (pDFA); dashed lines: correctly classified selected cases (pDFA). *p < 0.05 (Spearman's correlation; see table 2).

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