Language, which is part of what makes us human, is thought to have evolved within the last 100,000 years or so. Bolstering this relatively recent timeline, conventional wisdom holds that nonhuman primates are not capable of producing the five vowels that are universal to human languages.
“For 50 years, researchers have thought that only humans use a system of communication based on vowels and consonants,” says Joël Fagot, a comparative psychologist at Aix-Marseille University in Aix-en-Provence, France.
Now, however, new research overturns this long-held belief.
The assumption that only people can form vowels is based on the fact that the vocal box — or larynx — is relatively low in humans and relatively high in nonhuman primates. But then Louis Jean Boë, who specializes in the emergence of speech, discovered that human infants make vowel sounds even though their larynxes are high. As babies grow up, their larynxes descend to the low position of adults.
This made Boë and Fagot suspect that baboons could also make vowel sounds, despite their high larynxes. To find out, the researchers analyzed vocalizations of 15 Guinea baboons.
Their hunch turned out to be right. In a new study in PLOS ONE, Boë and Fagot report that baboons make five sounds that are similar to the five vowels of human speech. The researchers also found another unexpected similarity between baboon calls and human speech. “We were surprised that the baboons combined the vowel-like sounds in various ways,” says Boë, an engineer at Grenoble Alpes University in Saint-Martin-d’Hères, France.
This work indicates that the capacity for speech may be far older than previously thought. “Our findings suggest a very ancient origin of our articulatory capacities used to communicate with vocalizations,” Boë says. Human languages likely evolved from sound-making abilities already inherent in the closest ancestor shared by people and baboons, a monkey that lived some 25 million years ago.
Don’t expect to be able to hear many similarities between baboon calls and human speech, though. “Our perceptual system is not used to processing vowels when they are emitted at a fundamental frequency different from ours,” Fagot explains, adding that it is extremely difficult to hear the vowels in most baboon calls. The exception is the “wahoo” call, which carries over long distances: “We clearly hear a ‘wa’ and a ‘hoo’.”
Image Credit: William Warby, Flickr; Joël Fagot; Louis Jean Boë