Wild bonobos, the primates most closely related to humans, use a high-pitched type of call to communicate in a manner similar to infants, according to new research published in the journal PeerJ and led by researchers at the University of Birmingham in the UK.
Human infants, the researchers explained in a statement, are able to produce vocalizations in a wide range of emotional states and situations at a very early age. This ability is said to be one of the factors required for the development of language, and the study shows that wild bonobos are also able to produce a specific call type known as a “peep” in various situations.
Typically, animal vocalizations are produced in relatively narrow behavioral contexts linked to specific emotional states, such as the ability to express aggression or to warn about predators, the authors said. These new findings, however, show more human-like “functional flexibility” in the vocalizations of bonobos, clouding the division between humans and other primates.
In fact, the Birmingham researchers and colleagues from the University of Neuchatel found that wild bonobos can use their high-pitched “peeps” in many different positive, negative and neutral situations, such as when feeding, traveling, sounding an alarm, nesting or even grooming.
Foundations of speech, language capacity found in bonobos
Dr. Clay told redOrbit via email that research released several years ago found that human babies could produce a special type of vocalizations by the age of three months. These vocalizations are known as “proto-phones” and can be produced flexibly across various emotional states. She called this “an essential building block of human speech and language development.”
“This capacity was contrasted with other infant calls, such as screaming or laughing, and the calls of non-human primates, which were both said to be fixed or tied to specific emotional states (e.g. screaming when in a negative emotional state, laughing in positive state),” she explained. “We felt that the conclusion of fixed vocal signaling in non-human primates was unwarranted, based more on an absence of evidence rather than evidence of absence.”
So for their current study, Dr. Clay and her colleagues examined wild bonobos to see if they could find evidence of this same capacity for functional flexibility in other primates. They found that, “contrary to the conclusion of human uniqueness,” the peep call of bonobos is also flexible, and that this flexibility “suggests that in order to gain meaning, bonobos listening to the peeps may need to combine them with surrounding contextual or vocal information. These capacities also represent important foundations for human language.”
Dr. Clay said that these findings indicate that the ability to produce vocalizations in a flexible way across different contexts or emotional states is not unique to humans, and is in fact a trait that we share with our great ape relatives – and one that likely emerged before the evolution of human speech. While humans remain unique in terms of their speech and language capacities, she said, “the foundations underlying these abilities appear to be already present in the last common ancestor we share with great apes.”
“The more evidence we gather from studies of our great ape relatives, the more we learn that many of capacities thought to be uniquely human actually have their foundations firmly rooted in the primate lineage,” Dr. Clay concluded. “The next step is to conduct experiments to examine how bonobos respond to hearing peeps, what meaning they may extract from them and what additional contextual information they depend on in order to create this meaning.”
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Feature Image Credit: Zanna Clay/Lui Kotale Bonobo Project
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