by A chimpanzee puts its hand in front of a neighboring monkey in a video released by researchers. Is he showing off his muscles or asking for a friendly scratch? If you said he wants to scratch, congratulations: you understand “monkey.”
And you’re not the only one. According to a new study recently published in the journal PLOS Biology, many humans are good at understanding monkeys.
Although all apes vocalize to some extent, no other living ape species has evolved a human-like spoken language. In contrast, our primate cousins communicate using a language of body gestures.
Kirsty Graham and Catherine Hobaiter, both primary care physicians at the University of St. Andrews in Scotland was inspired to question the human understanding of ape language after realizing that 90% of the gestures used by chimpanzees and bonobos were shared by the two species, as well as 90% of those used by gorillas and orangutans.
“We wonder,” Graham said, “whether humans retain this ability to use and understand the great apes’ gestures.”
Graham and Hobaiter developed an online questionnaire to test people’s ability to understand various monkey gestures. Subjects watched a video of one of them and chose what the gesture meant from four options.
Thanks to an announcement of their study on BBC Radio 4 in Great Britain, the researchers had more participants than they expected: 5,656 people answered the questionnaire.
Respondents correctly identified the meaning of the gestures more than half of the time, with a rate of 52.1%. This is much higher than the 25% that would be expected if participants were guessing at random.
“This study represents an interesting method of obtaining a human interpretation of monkey gestures,” said Frans de Waal, a primary care physician at Emory University in Atlanta (USA), who was not involved in the research.
People also use non-verbal gestures. a librarian can silence a rowdy student by putting his finger to his lips, or a rude customer in a restaurant can wave a waiter away as if swatting a fly.
Babies, especially, are known to be gesticulators: another study found that 89% of the gestures used by 1- to 2-year-old babies were also used by chimpanzees of all ages.
But as we age, Graham said, subtle spoken language replaces many of these monkey-like gestures, so adults can no longer speak “Monkey” but can understand it, the new study shows.
In the spoken word, Graham said, “we can ask for things more specifically, more politely, more precisely.” This is why an adult wouldn’t (hopefully) ask for food by putting their hand in their mouth, but a baby would.
Perhaps the monkeys’ gestures are not completely lost in adult humans, but they are harder to recognize because they are “sometimes incorporated into other hand movements,” such as the gestures we sometimes make while talking, De Waal said.
In their article, Graham and Hobaiter point out that the entanglement of our gestures with our use of spoken language makes it difficult to find clear human uses of ape gestures.
Charlotte Wiltshire, a PhD student at St. Andrews, who is collaborating with the two researchers, is developing a machine learning program that could facilitate this effort.
“The dream is to one day automate video encoding,” Graham said, referring to the process of watching animal videos and noting observed behaviors. “We’ll have a trained model capable of detecting gestures. It doesn’t matter how much overlap there is between a chimpanzee’s gestures and our own,” Graham said. “Our ability to understand the language of apes highlights that we are more like them than different.”
“People are really cool, but we’re not unique in all our abilities,” Graham said.
De Waal agreed: “If you’ve ever seen human children playing with young apes, you’ll notice a lot of overlap in gestures and a high degree of mutual understanding and enjoyment, as if there were almost no barriers between them. “
Translated by Luiz Roberto M. Gonçalves
