Great ape's consonant and vowel-like sounds travel over distance without losing meaning

An Orangutan. Credit: Madeleine E. Hardus
Scientists have found that orangutan calls, which are believed to be the closest to the precursors of human language, can travel long distances in forest without losing their meaning. Researchers from the University of Warwick have found that this results in a question of the accepted mathematical model of the evolution of human speech.

Mathematicians have developed a model that predicts that humans used sounds to connect their calls to increase the likelihood of transferring a signal's contents to their recipients over distance. Signal quality decreases as you travel further, so it is suggested that humans used sound links to transmit information.

The University of Warwick's Department of Psychology collected empirical data in order to test the model. The sounds were selected from audio recordings of orangutan communication. At distances of 25, 50 and 75 meters, specific vowel-like and consonant-like signals were recorded and played back. Analyses were made of the quality and content received signals. These results were revealed in the Biology Letters study, "Orangutan Information broadcast via consonant and vowel-like calling breaches mathematical models of Linguistic Evolution", published today in Biology Letters.

Although the signal quality may have declined, the content was not affected even at long distance. The team found that the informational characteristics of calls were unaffected until the signal was no longer audible. This puts into question the accepted theory of language evolution.

The study was led by Dr. Adriano Lameira from the University of Warwick. He is an evolutionary psychologist. He stated:

"We used our audio data recording bank from our study of the orangutan in Indonesia. We chose the clear vowel and consonant sounds and played them back. Then, we re-recorded them in a rainforest setting over measured distances. This study was designed to examine the signals and see how they functioned together as a package. Because you cannot assess the error limit theory from a distance, this study is very interesting. It ignores other aspects such as gestures, postures, and facial expressions.

"The results indicate that these signals appear to be impervious of distance when it comes encoding information.

It challenges the current thinking that was based on the Harvard scientists' model 20 years ago. They concluded that signals used by our ancestors reached an error limit, which is the point at which a signal stops being meaningful after it has been received. They concluded that ancestors connected sounds together to increase content's chance of traveling long distances.

"We all know that sound decreases the farther you are from the source. This effect can be felt when you shout for a friend or relative. Although they don't hear everything you say, they can recognize that you are speaking to them and that your voice is being heard. We have demonstrated that even though the sound package has been distorted and separated, its content is not. This is a call to scientists to reexamine how language evolved.

Dr. Adriano Lameira used the orangutan call because they were first to deviate from the great lineage of great apes. However, they are the only great species which use the vowel sound and consonant sounds in a complex manner giving them a parallel to human speech.

His research team is now working to determine the meaning of the calls. This research involves combining all the orangutan calls and putting vowel and consonant sounds together to find meaning.

He stated that he didn't know the exact meaning of their words, but it is clear that they do use the same building blocks as language. While other animal sounds and signals may be more complex than human ones, they do not use the same building blocks. This is the exact component that the great apes use to build language. This gives us the analogy to human language.

"The Harvard model has been accepted for many years. If you asked a mathematician whether language origins are still a puzzle, they would say no. However, evolutionary psychologists continue to work on the problem. We haven't solved this puzzle, but we have gone further down the rabbit hole.

"We propose that mathematical models are applied to real-life data in order to see what we can create together."

Continue reading Voice control in an orangutan offers clues to early human speech

More information: Orangutan information broadcast via consonant-like and vowel-like calls breaches mathematical models of linguistic evolution, Biology Letters, .1098/rsbl.2021.0302 Journal information: Biology Letters Orangutan information broadcast via consonant-like and vowel-like calls breaches mathematical models of linguistic evolution,