Chiladas are highly sociable primates with a relatively large vocal range. The lip-smacking vocalizations of Chilada baboons may provide clues as to how speech originated.
Lip-smacking can be seen in many non-human primates, but only Chilada baboons (a terrestrial, Old World monkey Theropithecus gelada) vocalize while doing it. These vocalizations, known as "wobbles", can sound disconcertingly human - when Thore Bergman (the author of the paper) was observing Chilada in Ethiopia he frequently mistook the sound for someone trying to talk to him, only to find it was Chilada instead. Though other primates are known to make complex sounds, only Chilada vocalizations possess pitch and volume fluctuations similar to speech.
Previous research with macaques revealed that the facial movements involved in lip-smacking were very speechlike, indicating a precursor to speech. However neither macaques nor any other primate ever vocalized during these lip-smacks. The fact that Chilada vocalize during lip-smacks supports this hypothesis as a possible origin of speech (though likely not the only route to speech).
The function of the wobbles is not currently known. A social function seems likely, especially when comparing social complexity between Chiladas and their nearest relatives, baboons. Baboons, who don't vocalize as much or smack their lips, live in smaller and more short-lived social groups. Bergman is curious whether the wobbles allow Chilada to communicate things other monkeys can't.
Chilada baboons might have answer for children with autism, as human mirror mechanism for action understanding and imitation. Always good things come from the Promised Land. Because, everything grows with Love, Ethiopia.
To read the paper:
The social role of imitation in autism: