A chimp sticks his arm in front of his neighboring ape in a
video released by researchers. Is he showing off his muscles or asking for a
friendly scratch? If you said he wants to be scratched, congratulations: You
can understand ape.
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And you are not alone. According to a new study, published
recently in the journal PLOS Biology, many humans are pretty good at
understanding ape.
While all apes vocalize to some extent, no other living ape
species has developed humanlike spoken language. Instead, our primate cousins
communicate using a language of physical gestures.
Kirsty Graham and Catherine Hobaiter, both primatologists at
the University of St. Andrews in Scotland, were inspired to quiz human
understanding of ape language after noticing that 90 percent of the gestures
used by chimpanzees and bonobos were shared across those two species, as were
90 percent of those used by gorillas and orangutans.
“We’re then wondering,” Graham said, “if humans retain this
ability to use and understand great ape gestures.”
Graham and Hobaiter developed an online quiz testing
people’s ability to understand various ape gestures. Test-takers watched videos
of a gesture, then picked what they thought the gesture meant from four
options.
Thanks to a plug for their study on BBC Radio 4 in Britain,
the researchers had more participants than they expected: 5,656 people finished
the quiz. The respondents correctly identified the meaning of gestures more
than half the time, at a rate of 52.1 percent. That is much higher than the 25
percent that would be expected if participants were guessing randomly.
“This study represents an interesting method to get at human
interpretation of ape gestures,” said Frans de Waal, a primatologist at Emory
University in Atlanta, who was not involved with the study.
Humans use nonverbal gestures, too; a librarian might shush
a noisy patron with a silent finger to the lips, or a rude diner might
wordlessly shoo away a server as if swatting a fly. Babies, especially, are
known to be prolific gesturers: Another study found that 89 percent of the
gestures used by 1- to 2-year-old infants were also used by chimpanzees of all
ages.
But as we get older, Graham said, nuanced spoken language
replaces many of these simian gesticulations, such that adults can no longer
speak ape but can, as the new study shows, still understand it.
In spoken language, Graham said, “We can request things more
specifically, more politely, more accurately.” This is why an adult would
(hopefully) never ask for food by sticking their hand in your mouth, but a baby
might.
It may not be the case that ape gestures are completely lost
in adult humans, but rather that they’re more difficult to recognize because
they’re “sometimes embedded in other manual movements,” like the hand movements
we sometimes make while speaking, de Waal said.
In their paper, Graham and Hobaiter point out that the
intertwining of our gesturing with our use of spoken language makes finding
distinct uses of ape gestures by humans difficult. Charlotte Wiltshire, a
doctorate student at St. Andrews who is working with the two researchers, is
developing a machine learning program that could make this endeavor easier.
“The dream is to one day automate video coding,” Graham
said, referring to the process of watching videos of animals and marking down
observed behaviors. “We’ll have a trained model that can detect gestures.” No
matter what degree of overlap there is between a chimpanzee’s gestures and
ours, Graham said, our ability to understand ape language highlights that we’re
more similar to them than we are different.
“Humans are really cool, but we’re not unique in all of our
abilities,” Graham said.
De Waal agreed: “If you have ever seen human children play
with young apes, you will notice great overlap in manual gestures and a high
degree of mutual understanding and fun, as if there exists barely any barrier
between them.”
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