Ooh-ah Cathy Withers-Clarke/Alamy Stock Photo

Baboon grunts and barks have more in common with human speech than we thought. The monkeys routinely produce five of the distinct vowel sounds found in our languages.

Researchers typically link our ability to produce a range of vowels with the low position of the human voice box, or larynx, in the throat. Non-human primates have a high larynx, hence are thought to be incapable of producing many vowel sounds.

But according to Joël Fagot at Aix-Marseille University and Louis-Jen Boë at the Grenoble Alps University, both in France, this standard explanation is wrong.


They point out, for instance, that infants can produce a similar range of vowels to adults even though the larynx only begins to descend midway through childhood.

Fagot, Boë and their colleagues have now analysed 1300 baboon vocalisations, recorded at a primate research centre in Rousset-sur-Arc in southern France. They extracted vowel-like sounds from the calls and used software to identify the key resonant frequencies, or “formants”.

The lowest two formants — denoted F1 and F2 — are known to give a reasonable indication of the position of the tongue, and can help computers classify the associated vowel sound.

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The team discovered that male and female baboons each produce four vowel-like sounds. Females produce one that males don’t, and vice versa, so in total there are five distinct vowels. They correspond to the second syllable in “roses”, and the vowel sounds in “you”, “thought”, “trap” and “ah”.

Fagot says the work complements a study published last month by Tecumseh Fitch at the University of Vienna, Austria, and his colleagues. It concluded, through analysing macaque anatomy, that monkeys should theoretically be able to produce a range of vowel sounds.

“We believe that one of the major advantages of our study is that we worked on real vocalisations, which were spontaneously produced by baboons in a social context,” says Fagot.

But Philip Lieberman at Brown University in Providence, Rhode Island, is not convinced. He thinks the researchers have unwittingly processed the baboon calls in a way that accentuates the fundamental frequency of the call and its harmonics.

In most of their analysis, Lieberman says, Fagot and Boë have then misidentified these harmonics as the F1 and F2 formants, and as a consequence they have overestimated the baboons’ vowel-making capacity.

Fagot says it’s easy to make such an error, but he is adamant they did not. “We discarded any of the vocalisations for which the confusion between harmonic and formant would be possible,” he says.

Linguistic roots: The evolution of language

For Fagot, the findings raise fresh doubts about the link between the position of the larynx and the origin of spoken language. He thinks that its important features may have originated as far back as the common ancestor of monkeys and humans, which lived about 25 million years ago.

Fitch agrees with this assessment. “This study corroborates our argument that primitive vocal anatomy would not have been a hindrance to evolving spoken language,” he says. “It adds fuel to the fire burning down that old misconception.”

Johan Bolhuis at Utrecht University in the Netherlands says the results are interesting, but he doubts they will greatly alter our understanding of the origins of human language. “This is, in fact, additional evidence to show that with the ‘speech machinery’ being present, you do not automatically evolve language,” he says.

He says language as we recognise it is a recent (and probably initially non-verbal) innovation restricted to the human lineage. Over time, language then recruited pre-existing systems, most obviously speech. “Speech does not lead to language – rather language may be externalised as speech,” says Bolhuis.

A few other studies in recent years also suggest language made use of pre-existing systems. For instance, many of the genes that help us learn to talk are also active in some songbirds when they learn new songs – but birds haven’t developed language in the strictest sense, says Bolhuis.

Journal reference: PLoS One, DOI: 10.1371/journal.pone.0169321