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Great ape messages retain their meaning over a distance

The current model for explaining the origin of language is that human ancestors joined call sounds together in order to increase the chances that the signal’s content would carry over a distance to potential recipients. This model was developed by mathematicians who proposed that the linking together of sounds would effectively convey messages across distances, even if individual elements of the calls became degraded or distorted along the way. 

Researchers in the Department of Psychology at University of Warwick set out to test this model. They used recordings of orangutan calls from which they selected consonant-like and vowel-like signals. These were individually broadcast over the rainforest habitat and re-recorded at distances of 25, 50, 75 and 100 meters. The re-recorded sounds were then analyzed for quality and content. 

“We used our bank of audio data recordings from our studies of orangutan in Indonesia,” explained Dr. Adriano Lameira, an evolutionary psychologist who led the study. “We selected the clear vowel-like and consonant-like signals and played them out and re-recorded them over measured distances in a rainforest setting.”

“The purpose of this study was to look at the signals themselves and understand how they behaved as a package of information. This study is neat because it is only across distance that you can hope to assess this error limit theory – it disregards other aspects of communication like gestures, postures, mannerisms and facial expressions.”

The results showed that, although the quality of signals may degrade over distance, the message carried by the vowel-like and consonant-like signals was retained, even though they were not joined together with other sounds. The informational content of the calls actually remained uncompromised until they became inaudible. This is contrary to the prediction of the current model used to explain the origin of human speech development.

“The results show that these signals seem to be impervious to distance when it comes to encoding information,” explained Dr Lameira.

“It calls into question the existing thinking based on the model set out 20 years ago by Harvard scientists.  Their work assumes that the signals that our ancestors were using were reaching an error limit – a moment when a signal is received but stops being meaningful. They concluded that our ancestors linked sounds together to increase the chance of content travelling over distance.” 

“We know sound degrades the further away from the source you are. We have all experienced this effect when shouting for your relative or your friend. They don’t hear all the words you say – but they recognize you are talking to them and that it is your voice.”

“By using actual great ape communication sounds, which are the closest to those used by our hominid ancestors, we have shown that although the sound package is being distorted and pushed apart, the content remains unaltered. It’s a call to the scientific community to start thinking again about how language evolved.”

Orangutan calls were chosen by Dr. Lameira and his team because their sounds are thought to be the closest to the sounds used as precursors to human language. Orangutans were the first species to diverge from the great ape lineage but are the only great ape that uses vowel and consonant sounds in a complex way. 

“We still don’t know what they are referring to, but right now what is completely clear is that the building blocks of language are present. Although other animal sounds and signals are complex, they are not using the same building blocks. We are focused here on the building of language – exactly the component the great apes use. It gives us the parallel to human language,” explained Dr. Lameira.

“The Harvard model has been the accepted theory for years and if you ask a mathematician if language origins were still a puzzle they’d say no – but evolutionary psychologists are still working on it. But we haven’t solved the puzzle either – if anything we have just gone deeper down the rabbit hole.”

The results of the study are published in the journal Biology Letters.

By Alison Bosman, Staff Writer

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