The gestures used by infant humans for communication, and those used by baby apes — at comparable stages of communicative development — are remarkably similar, more so than was previously thought, according to new research from UCLA. This finding raises interesting questions about the origin of symbolic language.
The new research was done by analyzing and comparing the gesturing done by a female human infant, a female baby chimpanzee, a female baby bonobo — with the aid of video footage taken of the three. This is some of the first research to directly compare the development of communicative gestures across species. Both the chimpanzee and the bonobo are rather closely related to humans, very-likely more so than any other species.
“The similarity in the form and function of the gestures in a human infant, a baby chimpanzee and a baby bonobo was remarkable,” said Patricia Greenfield, a Distinguished Professor of Psychology at UCLA and co-author of the study.
The gestures in question, include: Pointing with fingers, reaching, pointing with the head, and raising the arms to let it be known that they want to be picked up.
The press release continues:
To be classified as communicative, a gesture had to include eye contact with the conversational partner, be accompanied by vocalization (non-speech sounds) or include a visible behavioral effort to elicit a response. The same standard was used for all three species. For all three, gestures were usually accompanied by one or more behavioral signs of an intention to communicate.
Charles Darwin showed in his 1872 book “The Expression of the Emotions in Man and Animals” that the same facial expressions and basic gestures occur in human populations worldwide, implying that these traits are innate. Greenfield and her colleagues have taken Darwin’s conclusions a step further, providing new evidence that the origins of language can be found in gestures and new insights into the co-evolution of gestures and speech.
The apes included in the study were named Panpanzee, a female chimpanzee (Pan troglodytes), and Panbanisha, a female bonobo (Pan paniscus). They were raised together at the Language Research Center in Atlanta, which is co-directed by Sue Savage-Rumbaugh, a co-author of the study. There, the apes learned to communicate with caregivers using gestures, vocalizations and visual symbols (mainly geometric shapes) called lexigrams.
The human girl grew up in her parents’ home, along with her older brother. Where the apes’ symbols were visual, the girl’s symbols took the form of spoken words. Video analysis for her began at 11 months of age and continued until she was 18 months old; video analysis for the two apes began at 12 months of age and continued until they were 26 months old. An hour of video was analyzed each month for the girl, the chimpanzee and the bonobo.
The researchers note that the lexigrams that the apes used were learned ‘naturally’ — as a result of social interactions, not through behavioral training.
The new research supports the ‘gestures first’ theory of the emergence of symbolic language. In their early life, all three individuals appeared to rely on gestural communication, before then gradually increasing their use of symbols — verbal language for the human infant and lexigrams for the apes.
“Gesture appeared to help all three species develop symbolic skills when they were raised in environments rich in language and communication,” said Gillespie-Lynch, who conducted the research while she was at UCLA.
Interestingly, the researchers noted that most of the human infant’s gestures were accompanied by vocalizations, but not the ape’s.
“This finding suggests that the ability to combine gesture and vocalization may have been important for the evolution of language,” Greenfield said.
The researchers “conclude that humans inherited a language of gestures and a latent capacity for learning symbolic language from the last ancestor we share with our chimpanzee and bonobo relatives — an ancestor that lived approximately 6 million years ago.”
The emergence of human language was simply the result of capacities that were already present in the common ancestor of the three species.
“Our cross-species comparison provides insights into the communicative potential of our common ancestor,” Gillespie-Lynch said.
The new research was just published in the open-access journal Frontiers in Psychology.