Lip-Smacking Primates May Offer Insight Regarding The Origin Of Human Speech

While working in the mountains of Ethiopia, Thore Bergman of the University of Ann Arbor said he often found himself looking over this shoulder to see who was talking to him. The answer, it turned out, was the gelada baboon.

With an estimated 100,000 to 200,000 left, the gelada baboon communicates through vocal lip-smacks that sound remarkably similar, as Bergman discovered, to human speech.

"It was unnerving to have primate vocalizations sound so much like human voices," the scientist said in a press release.

Then, a year ago, Bergman came across a paper in the journal Current Biology that proposed vocalization while lip-smacking may have been a possible first step to human speech.

If this were true, he figured, then a comparison of geladas' vocalizations, known as "wobbles," would likely match the structure of human speech.

Sure enough, Bergman found that the lips, tongue and hyoid moved with a speech-like 5 Hz rhythm when the monkey was lip-smacking, but, crucially, not when it was chewing. This measurement, 5 Hz is the stereotypical rhythm of human speech.

In short, both the gelada opened and closed certain parts of the mouth while communicating that it didn't when it was merely eating.

What's more, Bergman believes that besides being formed the same way, the monkeys' lip-smacking closely resembles the same purpose many humans use speech for - bonding.

"Language is not just a great tool for exchanging information; it has a social function," he said. "Many verbal exchanges appear to serve a function similar to lip-smacking."

Today the gelada faces several threats, including hunting by indigenous populations who use the monkey's mane for coming-of-age ceremonies. For this reason, the species has been listed as threatened by the U.S. Fish and Wildlife Protection Service since 1976. In all, they have a lifespan of approximately 19 years.