Prior to developing the capacity for speech, toddlers communicate their desires, demands and discontent using a diverse repertoire of physical gestures. As a new study shows, there’s a significant amount of overlap between the gestures employed by human children and those made by other ape species, a finding that’s casting new light on the origin of primate communication.
New research published this week in Animal Cognition is the first to classify gestures made by human children using the same technique that’s used to classify gestures made by other ape species, specifically chimpanzees.
Results show that toddlers between 12 to 24 months use nearly 90 per cent of the same gestures employed by juvenile and adult chimps, including hugging, jumping, stomping and throwing objects. The presence of this shared gestural repertoire, the researchers say, suggests these behaviours are innate — a legacy of our shared evolutionary history.
The authors of the new paper embarked on the study in hopes of exposing similarities and differences in the ways young humans use gestures compared to other apes, and to potentially unveil new insights into the development of human communication.
“Since chimpanzees and humans shared a common ancestor around 5-6 million years ago, we wanted to know whether our evolutionary history of communication is also reflected in human development,” Verena Kersken, a researcher at the University of Göttingen and the first author of the study, said in a University of St Andrews statement.
For the study, the researchers observed the gestures made by toddlers in their natural “habitat”, such as at home or at daycare, and with peers, relatives and caregivers present. Thirteen children in total were observed, six in Germany and seven in Uganda. The sample population came from two different cultures “to reduce bias from the impact of culture and native language on early gesturing,” write the researchers in the paper.
The chimpanzees, ranging in age from one to 51 years old, were observed in their natural habitat at the Budongo Forest in Uganda. Wild great apes have no vocal language, but they use about 80 different gestures. Recently, scientists created a compendiums of these gestures, called Great Ape Dictionary, to help decipher their meaning.
“Wild chimpanzees, gorillas, bonobos and orangutans all use gestures to communicate their day-to-day requests, but until now there was always one ape missing from the picture — us,” explained Catherine Hobaiter, a senior author of the paper and a scientist at the School of Psychology and Neuroscience at the University of St Andrews. “We used exactly the same approach to study young chimpanzees and children, which makes sense — children are just tiny apes.”
Gestures documented among toddlers included arm raises, stomps, claps, hugs, head shaking, grabbing and so on. In all, the toddlers made 52 distinct gestures, of which 46, or 89 per cent, were also documented among the chimpanzees. Like chimps, the toddlers used these gestures both singly and by stringing them together in a sequence.
“We thought that we might find a few of these gestures — reaching out your palm to ask for something or sticking your hand up in the air — but we were amazed to see so many of the ‘ape’ gestures used by the children,” said Hobaiter.
In terms of differences, the toddlers used pointing gestures more frequently than apes (weirdly, chimps struggle to grasp finger pointing, whereas dogs and wolves totally get it). Also, the practice of waving our hands to say hello or goodbye appears to be a distinctly human gesture, the researchers say.
The big takeaway of this paper is that, though many differences exist between us and our great ape relatives, humans have retained some shared behavioural aspects, which are expressed at an early stage in our development. These gestures, the authors say, likely play an important role for children before they develop the capacity for verbal speech. Here’s how the researchers put it in their study:
This apparently substantial overlap in the repertoire and use of gestures we observed in our sample suggests that before or at the early onset of language proper, human infants’ gestural repertoire is, at some level, largely shared with other apes, and they display it in a similar fashion: With indications of intentional use, in combination with different gestures, and flexibly towards more than one specific goal. ....
We suggest that these gestures have a long evolutionary history and may continue to be present in older language users, still existing alongside the other gestures that accompany speech or conventional gestures learned in a cultural context (for example: Waving to say good-bye, the "thumbs-up" gesture, or culturally specific forms of pointing).
Looking ahead, the researchers would like to repeat the study, but with a larger number of children and across a more culturally diverse set of individuals. They’d also like to extend the study to other great apes, like bonobos.
It’s important to point out, however, that these shared gestures, in addition to being a part of our shared evolutionary history, may also be a function of our shared body plans. Human toddlers and chimps, it can be argued, make the same gestures because they have such similar bodies.
So regardless of our shared evolutionary history, these gestures — such as reaching out for a desired object out of reach — simply make sense. At the same time, many of the gestures observed in this study could never be seen in dolphins, giraffes or platypuses, for example.
On that note, it would be fascinating to know if closely related non-primate animals, such as dolphins and whales, have their own versions of shared gestures. But that would be another study entirely.