‘Uniquely human’ language capacity found in bonobos

https://www.science.org/content/article/uniquely-human-language-capacity-found-bonobos
Human language can combine words to create
an infinite number of meanings—an ability
that gives language its expressive power and
sets it apart from the communication of other
animals. Now, researchers have found a more
modest version of this ability in bonobos,
our closest living relative. The apes can
combine different calls to create new
meanings, the team reports this week in
Science.
...
Previous studies have found that other animal
species can combine their calls, but only in
“trivial” combinations that simply add the
meanings together. Human language is much more
powerful: Speakers can combine words into more
than the sum of their parts. For instance,
“tall cook” is a trivial combination—it means
someone who is tall and a cook. But “good cook”
is not someone who is good and a cook: They
might be good at cooking, but terrible in
other areas—perhaps a dangerous driver. This
combination of words generates a new meaning.
...
To find out whether bonobos are capable of making
these “nontrivial” combinations, University of
Zürich (UZH) animal communication researcher
Mélissa Berthet spent 8 months following wild
bonobo groups in the Kokolopori Bonobo Reserve
in the Democratic Republic of the Congo. Every
day, she and her guides set out at about 4 a.m.
to find the bonobos before they left their
overnight nests, then tracked them all day.
Whenever she had a clear view of their
activities, she recorded every vocalization,
along with all its context: who made it, what
they were doing, how other animals responded,
and even what the weather was like. Any number
of more than 300 contextual features could be
linked with each call. Eventually, Berthet
started to understand some of what the animals
were communicating: “You see a vocalization
and then everybody moves … and it’s very
satisfying to be like, ‘Ah, I think I start to
get it,’” she says.
Berthet recorded 700 different vocalizations,
many of which were combinations of two
distinct calls, like “whistle and peep” or
“high hoot and low hoot.” To see whether the
animals were creating new meanings from these
combinations, the team borrowed an approach
from human language studies, statistically
analyzing how much context the vocalizations
shared with each other. (In human language,
words that occur in similar contexts tend to
be more closely related in meaning.)
Three combinations stood out: Their meanings
appeared different enough from those of their
constituent calls that they seemed to count
as nontrivial combinations. “High hoot and
low hoot” was one of these. “Low hoot,” the
team found, is often used in situations of
high excitement, and appears to mean
something like “I am excited.” “High hoot” is
used when bonobos want to alert others to
their presence and may mean “Pay attention to
me.” But the combination of the two calls
doesn’t simply mean “I am excited, pay
attention to me”; instead, it conveys a more
nuanced message. It is used specifically when
another individual is putting on an aggressive
display. The bonobo using this call
combination might be trying to stop the other
individual from displaying or get others in
the group to pay attention to the caller, the
authors suggest.
The findings suggest bonobos have a
“precursor” to the human capacity to combine
units of language to create new meanings, says
senior author Simon Townsend, a primate
communication researcher at UZH. Both bonobos
and humans may have inherited the ability from
our common ancestor some 7 million years ago,
he says.
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