Researchers from the University of Birmingham (UK) and the University of Neuchatel (Switzerland) have found that wild bonobos, our closest living relatives in the primate world, communicate using a high-pitched call type, or “peep,” that requires context to be understood. The findings, published in the journal PeerJ, echo the context dependent manner in which human babies also first communicate.
Study leader Dr Zanna Clay, from the University of Birmingham, said the bonobos’ peep calls are short, very high-pitched, and produced with a closed mouth. “They produce these calls in a wide range of situations, across positive, negative and neutral circumstances,” she explained.
Looking at the acoustic structure, the researchers found that the peep calls did not vary acoustically between neutral and positive contexts – for example, between feeding, travelling and resting. It is this similarity in calls made across different emotional contexts that echo the similarities found in human infant vocalizations.
Before language develops, human babies can produce a group of calls – called protophones – independent of their emotional state. These types of infant calls differ from commonly recognized calls such as laughter and crying, and the calls of most animals, which are thought only to be produced in certain contexts.
The type of communication the researchers observed in the wild bonobos could represent an important evolutionary transition from functionally fixed animal vocalizations – vocalizations that are tied to specific contexts or emotional states – towards human vocalizations, which seems to have appeared some 6 – 10 million years ago.