Chimpanzees (Pan troglodytes) have special grunt calls for particular types of foods. By studying what happened after two separate clans of adult chimps moved in together at the Edinburgh Zoo, a team of scientists led by Dr Simon Townsend from the University of Zurich has discovered that chimps can change those referential food grunts over time, to make them sound more like those of new peers.
Chimpanzees (Pan troglodytes). Image credit: Pelican / CC BY-SA 2.0.
The findings suggest that human language isn’t as unique as we thought in its ability to reference external objects with socially learned symbols.
“Our study shows that chimpanzee referential food calls are not fixed in their structure and that, when exposed to a new social group, chimpanzees can change their calls to sound more like their group mates,” said Dr Katie Slocombe from the University of York, the senior author of a paper published in the journal Current Biology.
Scientists had generally accepted that the acoustic structure of chimp calls was fixed, with the differences primarily a matter of the animals’ arousal state. That apparent lack of flexible control over their referential vocalizations had even been considered a key discontinuity with human language.
However, Dr Townsend, Dr Slocombe and their colleagues found that the acoustic structure of referential food grunts produced by two groups of adult chimpanzees converged over the course of three years, as its members got to know each other better. That acoustic convergence had nothing to do with individual food preferences, either.
The scientists used audio analysis to demonstrate the convergence of structure, but they could also hear the difference.
“We think it’s quite easy to hear how the two groups called in different ways for apples in 2010, and how by 2013 the Dutch individuals changed their grunts to sound more like Edinburgh individuals,” said co-author Dr Stuart Watson, also from the University of York.
The study provides the first evidence of non-human animals actively modifying and socially learning the structure of a meaningful referential vocalization from other members of their species.
Given the relatively short evolutionary distance between humans and chimpanzees – 5 to 7 million years – it also suggests that our most recent common ancestor with chimpanzees also shared this building block of language.
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