Chimpanzees choose hand clasps by cultural preference
The communities of chimpanzee, Pan troglodytes, that inhabit the Chimfunshi Wildlife Orphanage Trust in Zambia are genetically similar and live in four neighbouring communities, in the case of the animals chosen here.
GHC or the Grooming Hand Clasp is the mark of social greeting used by researchers (not literally) to investigate cultural differences between the communities. Two individual chimpanzees extend one arm overhead and clasp each other's upraised hands while grooming each other with the other arm.
Interestingly, the well-known Gombe chimpanzees of Jane Goodall fame do not engage in GHC. The mother is often the first to handclasp with her infant, indicating that behaviour will be passed on through the maternal line.
Two groups of the four used regularly performed the GHC while one group did begin a little clasping after the experimental period. The fourth group never engaged in any hand clasping, just like the Gombe animals. Most individuals of the groups performed the behaviour, with stable differences between individuals. Group one preferred the wrist to wrist technique (b) while group two tended to use the palm to palm style (a):
Grooming handclasp style examples: (a) palm-to-palm, (b) wrist-to-wrist; Credit: © Proceedings of the Royal Society B: Biological Sciences
The one-year interval between two concentrated studies was useful in establishing the stability of the style differences. The history of the behaviour in these groups goes back at least 9 years, thanks to previous studies. At least 30 years have passed since groups were first observed, however and 16 independent populations can be labelled as GHC-disposed nowadays.
Expansion of this distinctive behaviour being key, it was also important that over the period of study, naive chimpanzees took on the cultural style of their groups. Social learning of course was the "mechanism" thought to be acting.
This brings up the nut-cracking techniques used by chimpanzees. Tool use behaviour has social elements that could be passed on in the same way. The authors' opinion is clear. "We conclude that chimpanzees' social behaviour is not only motivated by innate predispositions and individual inclinations, but may also be partly cultural in nature."
I think this paper, Neighbouring chimpanzee communities show different preferences in social grooming behaviour, published in the Proceedings of the Royal Society B: Biological Sciences, proves their point, without labouring it.
Edwin J. C. van Leeuwen of the Max Planck Institute in the Netherlands and in Germany, and his colleagues, must be congratulated on a necessary job, well-performed and perfectly cultural!
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