The ability to produce vocalizations independent of certain situational or emotional states is thought to be required for the development of language. Human babies have been shown to be able to do this from a young age – as early as three or four months old, they display what’s known as “functional flexibility,” meaning that they make sounds that must be interpreted in context. It now seems that humans are not alone, and that bonobos can do this too.
“So we found that bonobos actually produce lots of different calls, and many of them do look a bit like emotional signals, so they scream when they’ve been attacked or they produce alarm calls when they’re experiencing alarm,” Dr. Zanna Clay, who led the new study published in PeerJ, told IFLScience. “But then we found this particular call called the “peep,” which seems to be used across many different contexts, and like what they showed for the babies, it’s produced independently of the emotional state.”
This finding that bonobos can alter the meaning of a noise depending on the context echoes what we see in human babies.
Wild bonobos feeding on lily pads. During feeding, bonobos frequently produce peep vocalizations as well as in other contexts. Credit: Zanna Clay/Lui Kotale Bonobo Project
The researchers investigated the situations in which the apes were using the peep noise, and compared its acoustic structure between the different contexts. They found that the structure didn’t vary at all, from positive situations, such as feeding, to negative ones such as aggression. This, the researchers claim, shows how the interpretation of the peep is entirely context dependent, and requires input from other stimuli. This is, in fact, what the scientists intend to look at next.
“There’re two ways that we think we know what they’re doing,” said Dr. Clay. “One is they’re probably combining it with contextual information in the situation, so if they see trees moving and then they hear a peep – that infers travelling.” The second way is something that they’ve already shown in bonobos, that they combine the peep with other calls to create different meanings.
By combing the calls, they actually manage to create more information than just the calls on their own. “So it’s sort of interesting from a syntax and speech evolution perspective, because it seems like the listeners need to integrate different bits of information,” explained Dr. Clay from the University of Birmingham.
This finding suggests that the ability for the development of language is not unique to humans, but is in fact shared with our closest living relatives. Dr. Clay suspects that because bonobos can do it, it’s probably likely that chimps can too, but maybe in a different way, and that there’s even evidence that orangutans also display this skill.