Scientists claim to have identified the missing link between human speech and monkey chatter.

Researchers analysed the distinctive "lip-smacking" sounds made by wild gelada baboons of the Ethopian highlands and found striking similarities to human speech.

Their noises are so human-like that Thore Bergman, an assistant professor with the University of Michigan, thought he heard people talking while he was hanging out with the creatures.

"I would find myself frequently looking over my shoulder to see who was talking to me, but it was just the geladas," he said. "It was unnerving to have primate vocalizations sound so much like human voices."

Male geladas smack their lips to produce a distincive "wobble" in their calls to females. These sounds follow a similar tempo to human speech.

Bergman suggested the research identified a "plausible" explanation of how human speech evolved.

He said: “The ability to produce complex sounds might have come first. Then, when we could do that, we could attach meanings and communicate in more sophisticated ways. Or it could be that, as we needed to communicate more, we developed an ability to produce a greater variety of sounds.”

All baboons smack their lips while eating and in a social context as well. They also produce several other vocalisations. It is believed monkeys living in large groups have stronger vocal skills.

“It’s a very complex social system. They have some of the largest groups of any primate,” Bergman said. “These very large group structures may be linked to vocal complexity. There’s some evidence across primate that bigger groups make more sounds.”

The research can be found in the journal Current Biology. According to the study's abstract, the gelada baboons' "independent evolution of a speech-like vocalization involving complex facial movements provides initial support for the hypothesis that lip-smacking was a precursor to the emergence of human speech". ®