Humans aren't the only species to speak baby talk, apparently. A new study published in the journal Peer J finds our closest living relatives communicate using high-pitched calls or "peeps" strangely similar to the sounds made by human babies before they can talk. Researcher Zanna Clay of the University of Birmingham was studying 39 bonobos in the Democratic Republic of Congo when she first heard the noises, made when the great apes' mouths are closed, per CNN and the Christian Science Monitor. Like most animals, bonobos use different "fixed calls" that relate to an event (like mealtime) or a mood (like fear) to communicate, but Clay and her team noticed the identical bonobo peeps were used in "just about every context you can imagine," whether it be positive, negative, or neutral, according to a press release.
"They peep when they're traveling, feeding, grooming, resting, nest building, playing, aggression, alarm—you name it," Clay says, noting you have to understand the context of the situation to understand a particular peep. One way to look at the apes' communication is to compare it to that of human babies. A baby's cry and laughter are much like fixed calls. But babies also make other sounds, known as protophones, which "are the building blocks of speech, in that they vary in function across different emotional states and contexts," Clay says. It appears the bonobos' peeps serve the same function, and this ability to communicate shows "many capacities thought to be uniquely human actually have their foundations firmly rooted in the primate lineage." (Bonobos also give away food to strangers.)