By using five years of observation on neighboring communities of chimpanzees at the Chimfunshi Wildlife Orphanage in Zambia, an international team of scientists has shown that chimpanzees are not only capable of learning from one another, but also use social information to form and maintain local traditions.
Common chimpanzee, Pan troglodytes (© Thomas Lersch / CC BY-SA 3.0)
The specific behavior that the team focused on was the ‘grooming handclasp,’ a behavior where two chimpanzees clasp onto each other’s arms, raise those arms up in the air, and groom each other with their free arm. This behavior has only been observed in some chimpanzee populations. The question remained whether chimpanzees are instinctively inclined to engage in grooming handclasp behavior, or whether they learn this behavior from each other and pass it on to subsequent generations.
At Chimfunshi, wild- and captive-born chimpanzees live in woodlands in some of the largest enclosures in the world. The team collaborated with local chimpanzee caretakers in order to collect and comprehend the detailed chimpanzee data.
Previous studies suggested that the grooming handclasp might be a cultural phenomenon, just like humans across cultures engage in different ways of greeting each other. However, these suggestions were primarily based on observations that some chimpanzee communities handclasp and others don’t – not whether there are differences between communities that engage in handclasping. Moreover, the early observations could have been explained by differences in genetic and/or ecological factors between the chimpanzee communities, which precluded the interpretation that the chimpanzees were exhibiting ‘cultural’ differences.
The new study, published in the Proceedings of the Royal Society B, shows that even between chimpanzee communities that engage in the grooming handclasp, subtle yet stable differences exist in the styles that they prefer: one chimpanzee group highly preferred the style where they would grasp each other’s hands during the grooming, while another group engaged much more in a style where they would fold their wrists around each other’s wrists.
“We don’t know what mechanisms account for these differences”, explained Dr Edwin van Leeuwen of the Max Planck Institute for Psycholinguistics, lead author on the study. “But our study at least reveals that these chimpanzee communities formed and maintained their own local grooming traditions over the last 5 years. Our observations may also indicate that chimpanzees can overcome their innate predispositions, potentially allowing them to manipulate their environment based on social constructs rather than on mere instincts.”
Apart from the different style preferences of the chimpanzee communities, the scientists also observed that the grooming handclasp behavior was a long-lasting part of the chimpanzees’ behavioral repertoire: the behavior was even transmitted to the next generation of potential handclaspers.
Grooming handclasp style examples. Left: two chimps engaging in a palm-to-palm grooming handclasp. Right: wrist-to-wrist grooming handclasp (© Mark Bodamer)
“By following the chimpanzees over time, we were able to show that 20 young chimpanzees gradually developed the handclasp behavior over the course of the five-year study. The first handclasps by young individuals were mostly in partnership with their mothers. These observations support the conclusion that these chimpanzees socially learn their local tradition, and that this might be evidence of social culture”, said study co-author Dr Mark Bodamer of the Gonzaga University in Spokane.
“Continued monitoring of these groups of chimpanzees will shed light on the question of how these group-traditions are maintained over time and potentially even why the chimpanzees like to raise their arms up in the air during social grooming in the first place”, Dr van Leeuwen concluded.
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Bibliographic information: Edwin J. C. van Leeuwen et al. Neighbouring chimpanzee communities show different preferences in social grooming behaviour. Proceedings of the Royal Society B, published online before print August 29, 2012; doi: 10.1098/rspb.2012.1543
