Chimpanzees can SPEAK, scientists claim after reviewing old footage - so, can you tell what these apes are saying?

Many scientists believe that the one thing that separates humans from our primate relatives is our unique ability to speak.

But new research suggests that the Planet of the Apes could be just around the corner, as scientists claim that chimpanzees can speak after all.

An international team of scientists reviewed footage of chimps who had been raised by humans in conditions which would now be considered unethical.

Their analysis of this footage, filmed in 1962, suggests that chimpanzees are capable of saying simple human words such as 'mama'.

This discovery could overturn old assumptions about ape psychology and show that the neural 'circuitry' of language evolved earlier than previously thought.

The question of whether apes are capable of speech is a topic that has divided generations of scientists.

Perhaps due to the importance of language in our sense of what makes humans unique, either side of the debate has attracted strong advocates.

Beginning in the 1900s, this debate culminated in a series of extremely unethical experiments in which people tried to raise chimpanzees like humans.

For example, the researchers reference the case of Keith and Catherine Hayes who adopted a chimp to raise in 1947.

The couple later claimed that the chimp, which they named Viki, had learned simple words like 'mama', 'cup' and 'up'.

However, very little direct evidence from these early trials survived and due to the trauma of separating chimps from their families, the results have largely been dismissed.

In their paper, published in Scientific Reports, the researchers argue that a lack of analysis of these older cases has led to a belief that apes are incapable of speech.

Lead author Dr Axel Ekström, of KTH Royal Institute of Technology, Sweden, told MailOnline: 'There has been an idea floating around neuroscience for a couple of years, that the chimp cortex might have been holding them back.'

The basic idea, Dr Ekström explains, is that humans have an overlap between the area of the brain responsible for moving the jaw and the region which controls the voice box.

'So, the idea was that this overlap unlocks syllabic speech of the kind we see in infants ("ba-ba-ba"), and which transitions in development to adult speech patterns,' says Dr Ekström.

The so-called 'Kuypers-Jürgens hypothesis' then suggests that since chimpanzees don't have this overlap they simply cannot produce speech like a human can.

By looking back at old footage of chimpanzees that have been raised around humans, Dr Ekström thinks he and his colleagues have found good evidence against this idea.

Specifically, the researchers uncovered two videos of chimps which appear to be capable of saying 'mama'.

The first shows a chimpanzee named Johnny who lived at the Suncoast Primate Sanctuary in Palm Harbor, Florida.

In the comments of the video, the original poster wrote: 'Johnny called everyone Mama. He was a marvelous animal and lived to 63 years of age.'

The second video shows a clip from a film titled 'Now Hear This! Italians Unveil Talking Chimp', which was released in 1962 as part of Universal Studios’ series of newsreels.

In the clip, a chimpanzee named Renata is tapped on the chin by a handler, who appears to prompt her to say something which sounds like 'mama'.

To test whether these utterances came close to human words, the researchers designed an online listening experiment.

The chimpanzee utterances were mixed in with clips of humans who had been diagnosed with Parkinson's disease.

Participants were told that all the clips were from speakers diagnosed with speech pathologies and asked to phonetically write down the sounds that they heard.

The researchers discovered that most of the participants agreed that Johnny and Renata were saying mama.

While Renata's vocalisations were generally clearer, a large number of participants still recorded Johnny making a sound featuring an 'a' sound.

The researchers argue this is clear evidence that chimpanzees do in fact have the jaw-voicebox 'coupling' required to make syllabic speech with consonants and vowels.

Dr Ekström says: 'The downstream conclusion from that is that either the cortical overlap is not crucial, or that chimpanzees possess it too.'

However, the researchers also point out that we are not likely to end up with the kind of talking chimpanzees you might recognise from 'Planet of the Apes'.

Even if chimpanzees do have the right kind of brain to learn new sounds, their tongues are long and flat which makes it difficult to move between speech sounds.

There is also a significant difference between learning to hear and repeat sounds and learning to speak a language.

Dr Ekström says that his paper shows that chimpanzees have this ability, known as 'vocal learning'.

But he adds: 'In our case, there is no evidence the chimpanzees understood the "point" of the word mama.

'That is, as far as we know, they weren't asking for their "mama", or addressing someone as "mama". These were sounds that to us carries a deep symbolic meaning, but it doesn't appear the chimpanzees were aware of that.'