A special feature of human language is that objects and events are named with socially learned symbols or words. Non-human primates like chimpanzees are arguably capable of producing alarm and food calls,that refer to objects in their environment. However so far researchers assumed, that the acoustic structures of these calls are an expression of their excitement and cannot be controlled by the chimpanzees. Now Simon Townsend, Evolutionary biologist from the University of Zurich has shown together with his English colleagues, that also chimpanzees can learn calls that refer to specific objects.
Grunt calls adapted after three years
Chimpanzees produce different grunt calls when finding different food items. In 2010 researchers from the Universities of Zurich and York got the opportunity to test, whether chimpanzees are capable of changing the structure of these grunt calls: A group of adult chimpanzees from Beekse Bergen Safari Park in the Netherlands were introduced to a group of chimpanzees in Edinburgh Zoo.
Under the lead of psychologist Katie Slocombe from the University of York the team of researchers observed that before the integration the two groups of chimpanzees produced acoustically different grunt calls for apple and furthermore had different preferences for apple. After the integration of the two groups, the researchers discovered that the acoustic structure of the grunt calls of the new group members had been adapted to the ones produced by the chimpanzees already living there: «Three years after the integration, the grunt calls of the new chimpanzees very much resembled the grunt calls produced by the Edinburgh chimpanzees. », says Simon Townsend. «The preferences for apple in these chimpanzees stayed the same during this period, but the grunt calls changed.»
Social proximity crucial for the change of «food calls»
For their study the researchers recorded the grunt calls for apple before the integration in 2010. They then recorded the same grunt calls one year after integration and again in 2013. The team of researchers found that the fact that they lived together for a year and heard the different grunt call for apple from the other group members was not sufficient to cause the changes in their call structure. Only in 2013, when analyses of the social network showed strong friendships between the two group members were formed, a change in the call structure could be observed.
According to Simon Townsend this is evidence, that chimpanzees are capable of actively changing and socially learning the structure of meaningful, object-specific calls. These findings could shed some light on the evolutionary origins of this basic ability: «The fact, that not only humans, but also chimpanzees learn object-specific calls suggests that our common ancestor that lived more than 7 million years ago also possessed this ability», concludes Simon Townsend.
Stuart K. Watson, Simon W. Townsend, Anne M. Schel, Claudia Wilke, Emma K. Wallace, Leveda Cheng, Victoria West and Katie E. Slocombe. Vocal Learning in the Functionally Referential Food Grunts of Chimpanzees. Current Biology. February 5, 2015. http://dx.doi.org/10.1016/j.cub.2014.12.032