DURHAM, United Kingdom — Chimpanzees use gestures, vocalizations, and facial expressions that are strikingly similar to those of human babies, new research reveals. They employ the same “sign language,” even though they diverged from a common ancestor that lived approximately 10 million years ago.
This study provides the first evidence of intentional communication outside human language, serving a variety of purposes such as initiating grooming and contact and facilitating sexual intercourse. Psychologists have found that this multifaceted communication helps chimpanzees convey their intentions more accurately across different situations, such as playing or fighting. The Durham University team explained that this ability evolves over the course of infancy and adolescence.
“When we think about human language, we know that it is a combination of different types of communication such as speech, facial expressions, and gestures. The way we communicate likely has deep evolutionary roots that are shared with some of our closest living relatives such as apes,” says lead author Dr. Emma Doherty in a media release. “Our study provides evidence that the way chimpanzees communicate with increased complexity as they get older is consistent with the development of communication we see in human infants.”
By examining the development of this complex form of communication in young chimpanzees, the researchers aim to understand more about the reasons behind it, shedding light on the potential evolutionary continuity between humans and other apes. This suggests that primate gestures with shared meanings extend to humans and could be biologically inherited.
The study is based on observations of 28 semi-wild individuals, between the ages of one to 11 years-old, at the Chimfunshi Wildlife Orphanage Trust sanctuary in Northern Zambia. Previous research on apes has primarily examined different forms of communication signals in isolation, including gestures, vocalizations, and facial expressions.
However, the researchers investigated how chimpanzees combined these forms of communication, offering new insights into how they develop. They found that our closest relatives consistently used standalone signals such as grunting, arm movements, or facial expressions across all ages and in various situations. However, as they aged, chimpanzees were more likely to combine different communication signals, particularly during responses to aggression or playful interactions.
Adolescent chimpanzees were also more prone to use a combination of different communication signals instead of individual gestures or expressions, especially in aggressive scenarios. The researchers suggest further studies on multimodal signals in wild primates to better understand how communication develops in different environments. This could illuminate how communication develops in apes and potentially enhance our understanding of the evolution of human communication.
“A lot of the focus of research so far into communication, both in humans and other animals, looks at individual communication signals independently, but we know humans combine these signals all the time from early infancy. As a close relative of humans, apes give us a snapshot into how these signals could have evolved into multimodal communications, ultimately culminating in human language,” says Professor Zanna Clay, the corresponding author of the study.
Sharing approximately 96 percent of human DNA, chimpanzees possess complex emotions, a high level of intelligence, unique fingerprints, and even a sense of humor, much like humans. However, their numbers have drastically decreased in West Africa over the past 25 years, and they are now classified as a critically endangered species. Wild chimpanzee mothers are killed for bush meat, and their babies are sold as high-value pets.
The study is published in the journal Animal Behaviour.
South West News Service writer Mark Waghorn contributed to this report.