Baby talk – a human superpower?

An almost universal phenomenon in humans is the use of child-directed speech, where caregivers communicate with children often involving a particular speech style also termed “baby-talk”. Numerous studies have linked the amount of child-directed speech children hear to better learning outcomes (e.g. vocabulary size or literacy skills). This practice seems to facilitate the acquisition of language. But how did this trait evolve?

To explore this, researchers from the University of Zurich (UZH) and the University of Neuchâtel (UNINE), members of the NCCR Evolving Language, and colleagues from universities in France, Germany and the US, have now investigated whether this trait is shared by other great apes.

Experts in baby-talk

In their study, which is on the cover of the journal Science Advances, biologists and linguists observed the use of “infant-directed vocal communication” among five species of great apes: humans, bonobos, chimpanzees, gorillas and orangutans. For this, they meticulously recorded the vocalizations the infants of great apes were exposed to in the wild.

Their results show that, by far, humans are the most frequent “baby-talk” users. “We were surprised by how little of this type of communication we actually observed in our closest living relatives,” explains Franziska Wegdell, UZH postdoc and one of the three first authors of the study.

But how would non-human great ape infants pick up any learned part of their communication system?

Learning by other means

Indeed, even in humans, there are other ways for infants to learn language. “We know that human infants are able to learn new words from overhearing surrounding speech from adults and from other children around them,” says Johanna Schick, UZH postdoc and co-first author. When comparing infant-surrounding communication among the five great ape species, the researchers found that all were exposed to similar levels, except for orangutans. It may be that, like humans, great apes also acquire aspects of their communication system socially but stemming from surrounding communication.

Furthermore, in their study, the researchers only focused on the amount of infant-directed vocal communication, and not on similar phenomena in other forms. “Since speech is a primary modality of language, we chose to begin our research by focusing on the vocal domain,” says Caroline Fryns from UNINE, the third co-first author. “But we know that non-human great apes direct gestures at their infants, and that some of these gestures even exhibit features also found in human infant-directed communication.”

Studying the evolution of child-directed speech

To unravel the evolution of language, an ideal approach would be to examine the language capacities of early humans. However, since language does not fossilize, we have no traces of these capacities in extinct hominin species. “For this reason, we turned our attention to our closest living relatives – non-human great apes – investigating their infant-directed vocal communication,” explains Franziska Wegdell.

The results of the study seem to indicate that the tendency to direct vocalizations at infants has been massively expanded in the human lineage.

Although only found in low levels in our great ape relatives, other species – including some monkeys, bats, cats or dolphins – have been shown to also direct vocalizations at their young. “To shed further light on the evolution of infant-directed communication, future work could compare how the characteristics and functions of this type of communication varies across species and why,” the researchers propose.

Link to pictures

https://drive.google.com/drive/folders/1oQMwlzJim9nLVrTs-iASPmfxwAz0NNK_?usp=share_link

More information

NCCR Evolving Language : https://evolvinglanguage.ch