As a group, primates aren't really known for their ability to create vocalizations, or sophisticated or complex sounds with their mouths. Yes, we humans have shown some talent in that area — what with the whole development of language and all that — but most apes and monkeys are unable to generate anything but the most basic of sounds.
That's strange, because our remarkable capacity for language really shouldn't have evolved in complete isolation from our cousin species. Even if most other primates don't show much talent for vocalization, we should still be able to find some vestiges of that ability elsewhere in our evolutionary family tree. But while other primates do move their lips and tongues in ways similar to the ways humans use these to create speech, most don't appear to have the necessary anatomy needed to actually generate language sounds.
Now, according to Dr. Thore Bergman of the University of Michigan, one monkey may have shed some much-needed light on this issue. The gelada, a monkey closely related to the baboon, makes an unusual call described in a BBC report as "a cross between a yodel and a baby's gurgle." The researchers refer to this call as a "wobble," and crucially the geladas make this call while also smacking their lips.
That may not sound like much, but it's what's known as a derived vocalization, meaning even their closest relatives, the baboons, are unable to make it. The researchers suggest that the geladas evolved this combination of vocalizations and facial movements in order to cope with their unusually large and vocal social groups. A similar evolutionary process — in which lip-smacking is combined with more complex vocalizations — could well have occurred in our earliest hominid ancestors, which means the geladas point to a kind of possible first step we took in our own ancient evolution from lip-smacking to language. Dr. Thoreson explained more in an interview with the BBC:
"Geladas make vocalisations that have some speech-like properties - it's the first time that that has been shown in a non-human primates... The problem is that no primates have ever been shown to produce vocalisations while making these facial movement. These primates can do the complex mouth movement and vocalise at the same time. In [human] speech, the onset of a syllable is loud and then there are quiet parts in between. If you were to look at a waveform where you see how speech gets louder and quieter across time, the time between those peaks happens at a fairly predictable frequency of 3Hz to 8Hz across different languages. The same thing happens with the gelada 'wobbles' - the periodicity has the same [frequency]."