Bonobos, our closest living relative among primates, may be able to give us an inside look at the evolution of human speech, new research shows.
Human infants are able, from an early age, to produce vocal sounds in a wide range of emotional states and situations. This ability is believed to be one of the aspects required for the development of language.
Now, researchers have found that wild bonobos can vocalize similarly. The findings challenge how we think about the evolution of communication and potentially move the dividing line between humans and other apes.
Typically, animal vocalisations happen in relatively narrow behavioural contexts linked to emotional states, such as to express aggressive motivation or to warn about potential predators. By contrast, humans exhibit ‘functional flexibility’ when vocalizing in a variety of situations.
Researchers from the University of Birmingham and the University of Neuchatel, conducted research on wild bonobos and discovered that in this species, individuals produce a call type, known as the ‘peep’, across a range of positive, negative and neutral situations, such as during feeding, travel, rest, aggression, alarm, nesting and grooming. Peeps are high-pitched vocalisations which are short in duration and produced with a closed mouth.
Author Zanna Clay said:
“More research needs to be done on our great ape relatives before we can make conclusions about human uniqueness. The more we look, the more continuity we find among animals and humans."
The paper’s authors, writing in an abstract, state:
“Peeps were produced in functionally flexible ways in some contexts, but not others. Crucially, calls did not vary acoustically between neutral and positive contexts, suggesting that recipients take pragmatic information into account to make inferences about call meaning. In comparison, peeps during negative contexts were acoustically distinct. Our data suggest that the capacity for functional flexibility has evolutionary roots that predate the evolution of human speech. We interpret this evidence as an example of an evolutionary early transition away from fixed vocal signalling towards functional flexibility."
Clay Z, Archbold J, Zuberbühler K. (2015) Functional flexibility in wild bonobo vocal behaviour. PeerJ 3:e1124 https://dx.doi.org/10.7717/peerj.1124
Photo: Zanna Clay/Lui Kotale Bonobo Project