Video: Examples of how orangutans produce mouth-made sounds simultaneously with voiced components. © Adriano R. Lameira and Madeleine Hardus
Two researchers have discovered that our reddish-brown relatives have a particular talent for producing sounds: Like some hip-hop musicians or songbirds, orangutans can produce two different tones at the same time with their voice and mouth. The scientists even see in this possible indications of the history of the development of tonal communication among the early members of our family tree.
Chimpanzees, gorillas, orangutans and humans: We belong to a group of primates called great apes – hominids. All members of this family are evolutionary descendants of a common ancestor that produced the four lineages millions of years ago. One of them spread to Asia and led to the orangutans, which are still hanging through the branches in the forests of the islands of Sumatra and Borneo.
Like all representatives of the great apes, orangutans have comparatively complex cognitive abilities. These also affect their communication: they are known to make sounds with special meanings. But the sounds that Adriano Lameira from the University of Warwick and his colleague Madeleine Hardus are now reporting on are something special. Their results are based on the acoustic analysis of vocalizations made by orangutans from two unconnected populations – from Borneo and Sumatra.
Heard something special
They report that they encountered a sonic phenomenon in both populations that they call biphonic calls. The sound analyzes showed that these are sounds that consist of two components. Humans usually produce them separately in speech: “We use lips, tongue and jaw to produce the unvoiced sounds of consonants. On the other hand, humans produce the voiced, open sounds of the vowels by activating the vocal folds in the larynx with exhaled air,” explains Lameira. Orangutans are also capable of making both types of sounds. However, as the researchers have now been able to show, they can also do this simultaneously.
Specifically, they determined this with two vocalizations, to which they were also able to assign a context: In conflict situations, male orangutans on Borneo produce a “chewing” sound with their mouth and a growling sound with their larynx at the same time. In contrast, in female orangutans in Sumatra, the team identified a biphonic call, consisting of a combination of a “kiss squeak” from the mouth and a “rolling sound” from the throat. This element of communication is apparently used to alert fellow animals to the presence of a potential predator, the scientists say. “The fact that we found biphonic calls in two different orangutan populations proves that this is a fundamental phenomenon,” says Lameira.
Interesting parallel
So far, the concept of songbirds is well known, the researchers say. But their anatomy and sound production system is special. Interestingly, however, with a little training we are also capable of pronounced biphonic sound production: “For humans, voiced and unvoiced noise production is unusual at the same time, but beatboxing is an exception,” says Hardus. This technique imitates the percussion rhythms of hip-hop music by using the mouth, throat and voice at the same time.
In their discovery, Lameira and Hardus now also see a possible meaning that goes beyond a curiosity among our animal relatives. “The mere fact that humans are anatomically capable of beatboxing raises the question of where this ability came from. Now there is an indication that the answer may lie in the evolution of our ancestors,” says Hardus. Lameira says: “It seems possible that early human speech sounded more like beatboxing before further development led to the consonant-vowel structure that we know today,” speculates the scientist.
Source: University of Warwick, professional article: PNAS Nexus, doi: 10.1093/pnasnexus/pgad182