Deciphering the secret language of primate gestures
Do you ever feel like gesturing with your hands helps you communicate? Have you ever wondered if any other animals do this? Hand motions and gestures can be an important part of communication, and not just for humans! Dr. Kirsty Graham (they/she), a research fellow at the University of St. Andrews, uses psychology and neuroscience to study the ways that primates like gorillas, chimpanzees, and orangutans use gestures to communicate with one another. This family of primates, called great apes, are the closest evolutionary relatives of humans. By understanding the way apes communicate with each other, Dr. Graham is discovering new secrets about the origins of human language.
Talk to the hand
In human communication, gestures are movements of body parts that help a listener understand what you’re trying to say. For example, if someone asks “how are you?” you may respond by saying “I’m good,” or giving a thumbs up, or both. This is the type of gesture that can vary across cultures – a thumbs up is a friendly gesture in North America, but can actually be really rude elsewhere in the world!
Another kind of communicating with gestures is the way that babies communicate before they learn how to speak. For example, a baby might use a grabbing motion to indicate that they want something. This type of gesture is more universal - these gestures precede language skills and are understood across human cultures.
Are gestures a kind of sign language?
While communicating with gestures might seem similar to sign language, they’re not the same thing! Sign languages are a family of languages, used primarily by people who are deaf or hard of hearing, that are constructed from physical motions instead of spoken words. Sign languages, just like spoken languages, have vocabulary and grammar. Gestures, on the other hand, are more abstract. Individual gestures don’t necessarily correspond to specific words, and their meanings are context dependent.
But humans aren’t the only animal that uses our hands to communicate! It turns out that large primates like chimpanzees, gorillas, or orangutans also communicate to each other with gestures. While gestures in human communication often serve to supplement spoken or signed language, gestures in primates are their own form of communication, similar to how babies communicate before they know how to talk. Primates use gestures to intentionally communicate specific messages, often directed at certain individuals, but the meanings of these gestures can be flexible. One gesture might be used to communicate a desire to mate, a desire to play, or a desire for social bonding. The differences between these meanings are understood based on who is part of the conversation. For example, a mature male gesturing at a mature female is understood as a desire to mate, but the same gesture coming from a young ape would indicate a desire to play.
Some of these gestures might even make sense to you! For example, apes have been known to fling their hands in a “go away” gesture that is very recognizable to humans. Some of Dr. Kirsty Graham’s research has focused on understanding just how well humans can understand ape gestures. They recently conducted a study with nearly 20,000 participants that showed that humans are surprisingly good at understanding ape gestures. Although scientists still don’t know why humans are so good at it, the answer might lie in our evolutionary history. It’s possible that early humans communicated with similar gestures to modern-day apes, and that our brains have retained the ability to understand this kind of communication.
But human communication is not invariable. Even within the same language, different groups can have different dialects. Dialect is a broad term that refers to differences in communication between groups, like differences in vocabulary, grammar, and pronunciation of words. They can most obviously be seen in regional variations in a language, like how someone from New York will speak English differently compared to someone from Texas.
And it turns out that “dialects” can even show up in different animal populations. Dr. Graham’s research has identified the existence of dialects in chimpanzee gestures. They’ve studied the ways in which apes from different social groups communicate using similar but different gestures. Specifically, they conducted a recent study, led by University of St. Andrews PhD researcher Gal Badihi, on a family of gestures called leaf-modifying gestures. These gestures are called “leaf-modifying” because they involve manipulating leaves to communicate. There are four main types of leaf-modifying gestures that Dr. Graham and their team identified: leaf-clip, leaf-tear, leaf-pull, and leaf-drop. These gestures all involve ripping or dropping leaves in similar but distinct ways.
This family of gestures is perfect for studying cultural differences in chimps because they’re similar but distinct gestures that appear to all be used to communicate a desire to mate when used by adult male chimpanzees. So if one group of chimps shows a preference for a certain type of leaf-modifying gesture over another, that might point to a cultural difference.
Dr Graham studied two neighboring communities of chimpanzees in Uganda, called the Waibira and the Sonso, who live next to one another in the same forest. They found that although both communities used leaf-modifying gestures, the Waibira used all four forms of leaf-modifying gesture and the Sonso had a strong preference for the leaf-clip gesture. Because both groups use the gesture to communicate the same meaning, this variation can be understood as a dialect of the same gesture.
How can we listen in on animal conversations?
Dr. Graham’s research takes a unique approach to the intersection between human and primate communication. They use insights from the study of human language to better understand how apes communicate, in addition to using ape communication to understand how human language might have evolved. This means that they do some studies that involve humans, like measuring how well humans understand ape gestures, and some studies that require observing primates.
Dr. Graham has focused on studying chimpanzees and bonobos in the wild. These primates live in communities in the forest, meaning that researchers are able to continually study the same group of apes for many years – one community of bonobos that Dr. Graham studies has been monitored by researchers for 50 years! A lot of earlier research on ape communication was done on primates in captivity. However, researchers have learned that primate communication is very context-dependent, meaning that apes in captivity behave very differently than they do in the wild, so studying apes in the wild is the best way to understand their communication patterns.
Studying apes in the wild presents many challenges. It’s really difficult to monitor every single interaction apes have, which means it’s hard for scientists to be sure that a certain community doesn’t do something – what if the scientists just missed it? Scientists have had to employ techniques for understanding what happens when they’re not observing. For example, when studying leaf-modifying gestures, scientists can observe the pieces of leaf left behind to infer what gestures happened when they weren’t observing. Modern technology is also very important for this research. Video recording allows researchers to gather data even when the scientist isn’t present, by setting up what’s called a camera trap. This is a camera that can be hidden in the environment and turn on to record when triggered by motion or sound. Video recording also allows researchers to do extensive data analysis even long after the data was recorded. For example, for Dr. Graham’s research on dialects, they used video data recorded by other scientists and were able to carefully analyze the videos to make observations.
Dr. Graham’s research has been an amazing insight into the way primates think and communicate. By listening in on their conversations with each other, we’re getting glimpses into the way great apes like chimpanzees view the world around them. And thanks to Dr. Graham’s work, we’re realizing just how much we have in common with our primate relatives.
Written by Ashley Cavanagh
Edited by Manasvi Verma, Caroline Martin, and Taylor Contreras
Animations by Helena Almazan, based on illustrations in Dialects in leaf-clipping and other leaf-modifying gestures between neighbouring communities of East African chimpanzees by Gal Badihi et al.
Other contributions by Yanting Tang
Sources and Additional Reading
Are ape gestures like words? Outstanding issues in detecting similarities and differences between human language and ape gesture by Catherine Hobaiter, Kirsty E. Graham and Richard W. Byrne
Women in Ecology and Evolution Podcast, Episode 6 by Kirsty MacLeod
Learning more about sign languages and ape gestures!
Define (5-10 minutes): What are sign languages and how are they used? Sign languages are visual languages that use a combination of hand gestures, facial expressions, and body movements to convey meaning. They are used by people who are deaf or hard of hearing to communicate with one another, as well as with hearing individuals who have learned the language. Sign languages are diverse and have their own unique grammar and vocabulary, and are recognized as official languages in many countries. To learn more about sign language alphabets, take a look at this worksheet to learn alphabets! Practice what you’ve just learned by decoding the sentence in this worksheet.
Create (30-60 minutes): In other areas of her research, Dr. Kirsty Graham has also focused on identifying different chimpanzee individuals. To start with an easier task, you can recognize different animal species by creating your own animal masks! Print out and color these masks to create your own animal kingdom!
Explore (30-60 minutes): As explained in the article, the non-verbal tools that apes use to communicate with one another are called gestures, which are more abstract forms of communications compared to sign languages that adult humans use. Watch this video collected by Dr. Graham’s team to learn more about ape gestures. What gesture is the chimp in the video using? Find out the answer by matching this with the list of gestures given below. Can you decode what the chimpanzee is trying to communicate by shaking tree leaves? Play this great ape dictionary game and see how well you do!