Summary: Child-directed speech, or “baby talk,” plays a crucial role in language development and is a near-universal human behavior. Researchers investigated whether this vocal strategy is shared with our closest relatives, the great apes, and found that humans use infant-directed speech far more frequently.
Although all great ape infants were exposed to similar surrounding vocalizations (except orangutans), direct vocalizations to infants were rare. This suggests that while social learning is present across species, human infant-directed speech may be a uniquely evolved trait that helped shape our advanced language abilities.
Key Facts:
- Human Uniqueness: Humans overwhelmingly dominate in use of infant-directed speech compared to great apes.
- Learning Environment: Great ape infants hear surrounding vocalizations, but few are directed specifically at them.
- Evolutionary Clue: The expansion of infant-directed vocalization may be a key turning point in human language evolution.
Source: University of Zurich
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.
About this evolutionary neuroscience research news
Author: Melanie Nyfeler
Source: University of Zurich
Contact: Melanie Nyfeler – University of Zurich
Image: The image is credited to Neuroscience News
Original Research: Open access.
“The evolution of infant-directed communication: Comparing vocal input across all great apes” by Franziska Wegdell et al. Science Advances
Abstract
The evolution of infant-directed communication: Comparing vocal input across all great apes
Human language is unique among communication systems since many elements are learned and transmitted across generations.
Previous research suggests that this process is best predicted by infant-directed communication, i.e., a mode of communication directed by caregivers to children.
Despite its importance for language, whether infant-directed communication is unique to humans or rooted more deeply in the primate lineage remains unclear.
To assess this, we investigated directed and surrounding vocal communication in human infants and infants of wild nonhuman great apes.
Our findings reveal that human infants receive dramatically more infant-directed communication than nonhuman great ape infants.
These data suggest that the earliest hominins likely relied more on surrounding communication to become communicatively competent, while infant-directed vocal communication became considerably more prominent with human language.
