What do monkey gestures say about human language? Some argue the origin of human language lies in vocal calls while others nod towards gestures.
A bonnet macaque shows its rear to its grooming partner. Credit: Shreejata Gupta and Anindya Sinha
Animals do the most amazing things. Read about them in this series by Janaki Lenin.
If my husband wanted his back scratched, he’d instruct, “Little bit to the right. Go up.” Being humans endowed with language, we can communicate. People with hearing and speech disabilities use hand signals. Linguists use the term ‘reference’ for such verbal and sign communication. Researchers from India now reveal how bonnet macaques communicate without words.
An adult male bonnet macaque parted the fur of a female, picking nits and removing tangles. The latter held her tail out, and the male immediately started examining it. She displayed referential gesturing, like our use of words, say researchers.
When primates move their hands, heads, or bodies to signal to each other, it’s called a referential gesture, Shreejata Gupta, the main author of the paper, told The Wire. Such communication however simple requires complex cognitive ability until now thought to be possessed only by chimpanzees and bonobos in the wild.
In Kibale National Park, Uganda, wild chimpanzees scratch the part of their body where they’d like to be groomed. Their partners appear to know what the gesture means and proceed to comb the indicated spot. Many other species of primates gesture in captivity, but they haven’t been seen doing so in the wild.
Much of our understanding of gestural communication and the evolution of language is based on studies of African apes. “Other non-ape primate species have been largely ignored in this context,” says Gupta.
Gupta, then a doctoral student, and her supervisor, Anindya Sinha, of the National Institute of Advanced Studies, Bengaluru, say bonnet macaques are the only wild monkey species known to use gestures to communicate with their mates. She studied four troops of macaques for a year and a half at Bandipur National Park, Karnataka.
The researchers noticed the macaques using four distinct gestures to show where they wanted to be groomed. These included changing the position of the body or a body part, moving head or neck, and presenting their rear ends. Their partners got the message nearly 95% of the time. In the rest of the cases when their mates didn’t respond correctly, the macaques persistently indicated the itchy spot until their partners paid attention to it.
A sceptic might say the groomers poked around the closest body part. But the researchers show that on some occasions, the monkeys combed through the indicated section that was farther away from them.
A gesture has no value if the other animal doesn’t understand it. “When one macaque offers a body part, the other stops grooming and reaches the indicated spot, often putting itself in an awkward position,” Anindya Sinha told The Wire. “This is the clinching evidence for intentional referential gestures.”
Although the study’s subjects belonged to different troops, their gestures were similar. Perhaps, these actions are typical of the species, says Gupta. But each troop used some postures more frequently than others, reflecting local socio-ecological conditions.
Changing the body’s orientation was the most popular posture among adult males and females. In a gesture identical to the chimpanzees at Kibale, an adult male macaque scratched his lower torso to show he wanted to be groomed there. Adult females also bend down while positioning their rears for grooming. Macaques typically pose in this manner when being submissive and showing their readiness to mate. The researchers say this posture is neither submissive nor related to courtship.
“In dominance and sexual contexts, there are other visual and auditory gestures,” says Sinha. “Here, it occurs in the middle of a grooming session. When the macaque-being-groomed raises its back, it doesn’t look at its partner nor does it use other gestures.”
Professor Richard Byrne of the University of St. Andrews, U.K. agrees with the researchers. “The researchers say the groomers do change their grooming to the new site that is held up in their faces. So they must realise that the groomee would like it groomed next. I’m sure they are good at imagining how the groomee feels, and they wouldn’t be grooming them if they didn’t want to help maximally.” Professor Byrne wasn’t involved in the study.
Only adults were adept at signalling and understanding the signals. Perhaps youngsters develop these skills as they grow, not unlike human children learning to point.
Gupta and Sinha suggest this form of communication may have arisen in a two-step process. First, by moving its body, the macaque being groomed becomes aware of a spot that needs attention. Then, it may use the same movement to gesture to another to show that spot.
Psychologist Joaquim J. Veà and primatologist Jordi Sabater-Pi, who studied bonobos, say referential gestures may develop in animals that groom and bond within complex societies. Primates are not unique in this, ravens of the Austrian Alps point with their beaks to communicate with other ravens.
What do monkey gestures say about human language? Some argue the origin of human language lies in vocal calls while others nod towards gestures. There isn’t enough data to reconcile the two theories. But psychologists Katja Liebal and Josep Call suggest mirror neurons enable macaques to perform an action and recognise its meaning. These neurons are located in that part of the macaque brain that corresponds to the Broca’s area in the frontal lobes of humans. This is the seat of language, producing and understanding speech. So bonnet macaque gestures may have a lot to do with the evolution of human language.
The authors say their observations are preliminary. Gupta intends to continue observing bonnet macaques and investigating their use of gestures. When I hit the right spot, my husband goes, ‘aah,’ in contentment. If the grooming macaque cared to look, it might be rewarded with the half-closed eyes of its blissful partner. Some even fall asleep.
The study was published in the journal Animal Cognition on July 9, 2016.
Janaki Lenin is the author of My Husband and Other Animals. She lives in a forest with snake-man Rom Whitaker and tweets at @janakilenin.
