SCIENTISTS have taken a step towards solving one of the longest-standing puzzles of evolution, after discovering our nearest primate relatives communicate using the same rhythms as we do.

Chimpanzee signals involving a quick succession of mouth open-close cycles have been identified at a rhythm of about five cycles/second (5Hz) - the same as every human spoken language.

The gestures, or lip smacks, with the “speech-like signature” have previously been noted in monkeys and other primate communication including gibbon song and orangutan consonant-like and vowel-like calls.

But until now, there was no evidence among African apes, such as gorillas, bonobos and chimpanzees, which are related much more closely to humans.

The breakthrough, by scientists at the University of St Andrews, in collaboration with the Universities of Warwick and York, is seen as a 'critical step' towards a possible solution to the puzzle of speech evolution.

It shows there has most likely been a continuous path in the evolution of primate mouth signals with a 5Hz rhythm, proving that evolution recycled primate mouth signals into the vocal system that became speech.

Dr Cat Hobaiter, a field primatologist and lecturer in the School of Psychology and Neuroscience at the University of St Andrews, said: "We have so many spoken languages, but they all have a common rhythm. Fascinatingly, this same rhythm seems to run through our primate family tree.

"Human spoken language is sodifferent to anything we find in the rest of the animal kingdom, but we have so many other ways of communicating information, such as body language and facial expressions, that are similar to animal communication.

“Language didn’t replace all of those other systems of communication - we still have them. All of the animal kingdom, including humans, use basic signals, body language and gestures.

“One of the things we’ve never been able to do is say where language came from - this extra amazing system that gave us Shakespeare and poetry and astrophysics.

“This type of signal in the primates, the monkeys and chimpanzees, has something in common with language and maybe that is one of the foundation stones on which we started to build.”

The paper “Chimpanzee lip-smacks confirm primate continuity for speech-rhythm evolution" is published today in the journal Biology Letters.