The vocal lip-smacks that gelada baboons make in friendly encounters are surprisingly similar to human speech, according to a new study.
The research lends support to the idea that lip-smacking, a behaviour that many primates show during amiable interactions, could have been an evolutionary step toward human speech.
The geladas, which live only in the remote mountains of Ethiopia, are the only nonhuman primate known to communicate with such a speech-like, undulating rhythm.
Calls of other monkeys and apes are typically one or two syllables and lack those rapid fluctuations in pitch and volume.
"Our finding provides support for the lip-smacking origins of speech because it shows that this evolutionary pathway is at least plausible," said Thore Bergman of the University of Michigan in Ann Arbor.
"It demonstrates that nonhuman primates can vocalise while lip-smacking to produce speech-like sounds," Bergman said in a statement.
Bergman has now analysed recordings of the geladas' vocalisations, known as "wobbles," to find a rhythm that closely matches human speech.
In other words, because they vocalise while lip-smacking, the pattern of sound produced is structurally similar to human speech.
In both lip-smacking and speech, the rhythm corresponds to the opening and closing of parts of the mouth. What's more, Bergman said, lip-smacking might serve the same purpose as language in many basic human interactions - think of how friends bond through small talk.
The study was published in the Cell Press journal Current Biology.
