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Bonobos use a combination of calls to encourage peace with their partner during mating rituals, research suggests.
The discovery is part of a study that suggests our close evolutionary cousins can string together vocalisations to produce phrases with meanings that go beyond the sum of their parts – something often considered unique to human language.
“Human language is not as unique as we thought,” said Dr Mélissa Berthet, the first author of the research from the University of Zürich.
Writing in the journal Science, Berthet and colleagues said that in the human language, words were often combined to produce phrases that either had a meaning that was simply the sum of its parts, or a meaning that was related to, but differed from, those of the constituent words.
“‘Blond dancer’ – it’s a person that is both blond and a dancer, you just have to add the meanings. But a ‘bad dancer’ is not a person that is bad and a dancer,” said Berthet. “So bad is really modifying the meaning of dancer here.”
It was previously thought animals such as birds and chimpanzees were only able to produce the former type of combination, but scientists have found bonobos can create both.
The team recorded 700 vocalisations from 30 adult bonobos in the Democratic Republic of the Congo, checking the context of each against a list of 300 possible situations or descriptions.
The results reveal bonobos have seven different types of call, used in 19 different combinations. Of these, 15 require further analysis, but four appear to follow the rules of human sentences.
Yelps – thought to mean “let’s do that” – followed by grunts – thought to mean “look at what I am doing”, were combined to make “yelp-grunt”, which appeared to mean “let’s do what I’m doing”. The combination, the team said, reflected the sum of its parts and was used by bonobos to encourage others to build their night nests.
The other three combinations had a meaning apparently related to, but different from, their constituent calls.
For example, the team found a peep – which roughly means “I would like to …” – followed by a whistle – appeared to mean “let’s stay together” – could be combined to create “peep-whistle”. This combination was used to smooth over tense social situations, such as during mating or displays of prowess. The team speculated its meaning was akin to “let’s find peace”.
The team said the findings in bonobos, together with the previous work in chimps, had implications for the evolution of language in humans, given all three species showed the ability to combine words or vocalisations to create phrases.
“The cognitive building blocks that facilitate this capacity is at least 7m years old,” said Dr Simon Townsend, another author of the research. “And I think that is a really cool finding.”
