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Chimps found to develop “social traditions”

Aug. 29, 2012
Courtesy of the Max Planck Society
and World Science staff

Chim­panzees are ca­pa­ble of de­vel­op­ing new, lo­cal “so­cial tra­di­tions,” ac­cord­ing to sci­en­tists who have in­ves­t­i­gated mu­tu­al groom­ing among sev­er­al groups of chimps.

The research col­la­bora­t­ion be­tween Gon­zaga Uni­vers­ity in Wash­ing­ton state and the Max Planck In­sti­tute for Psy­cho­lin­guis­tics in the Neth­er­lands in­di­cates that the way chimps groom each oth­er varies by com­mun­ity. 

Two chimpss en­gage in a palm-to-palm groom­ing hand­clasp. (Cred­it: Mark Bo­da­mer)


A un­ique “groom­ing hand­clasp” re­veals the dif­fer­ence, sci­en­tists ex­plain. In this ac­ti­vity, two chimps clasp each oth­er’s arms, raise those arms up in the air, and groom each oth­er with the free arms. This has only been seen in some chimp popula­t­ions, re­search­ers said. The ques­tion has been wheth­er chim­panzees are in­stinc­tively in­clined to en­gage in groom­ing hand­clasps, or wheth­er they learn it from each oth­er and pass it on to sub­se­quent genera­t­ions.

The scientists con­ducted ob­serva­t­ions be­tween 2007 and 2012 at the Chim­fun­shi Wild­life Or­phan­age Trust in Zam­bia. At Chim­fun­shi, a mix of wild- and captive-born chim­panzees live in wood­lands in some of the larg­est en­clo­sures in the world.

Pre­vi­ous re­search had sug­gested that the groom­ing hand­clasp might be a cul­tur­al phe­nom­e­non, just like hu­mans across cul­tures en­gage in dif­fer­ent ways of greet­ing each oth­er. But this idea was mainly based on the ob­serva­t­ion that some chimp com­mun­i­ties hand­clasp and oth­ers don’t – not wheth­er there are dif­fer­ences be­tween com­mun­i­ties that en­gage in hand­clasping. More­o­ver, sci­en­tists said, the early ob­serva­t­ions could have been ex­plained by dif­fer­ent ge­net­ic and/or ec­o­log­i­cal fac­tors among the chimp com­mun­i­ties, rath­er than “cul­tur­al” dif­fer­ences.

The new re­search sug­gests that even be­tween chimp com­mun­i­ties that en­gage in the groom­ing hand­clasp, sub­tle yet sta­ble dif­fer­ences ex­ist in the styles that they pre­fer. One group was found to pre­fer a style where they would grasp each oth­er’s hands dur­ing the groom­ing, while anoth­er group pre­ferred to fold the wrists around each oth­er’s wrists.

“We don’t know what mech­a­nisms ac­count for these dif­fer­ences,” said re­searcher Ed­win van Leeuwen of the Max Planck In­sti­tute. “But our study at least re­veals that these chim­pan­zee com­mun­i­ties formed and main­tained their own lo­cal groom­ing tra­di­tions over the last five 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 re­search team al­so ob­served that the groom­ing hand­clasp was a long-lasting part of the chim­panzees’ be­hav­ioral rep­er­toire: the be­hav­ior was even trans­mit­ted to the next genera­t­ion of po­ten­tial hand­claspers.

“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 col­la­bo­ra­tor Mark Bo­damer of Gon­zaga Uni­vers­ity.

“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,” van Leeuwen added.


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Chimpanzees are capable of developing new, local “social traditions,” according to scientists who have investigated mutual grooming among several groups of chimps. The collaboration between the Gonzaga University in Washington state and the Max Planck Institute for Psycholinguistics in the Netherlands indicates that the way chimps groom each other varies by community. A unique “grooming handclasp” reveals the difference, scientists explain. In this activity, two chimps clasp each other’s arms, raise those arms up in the air, and groom each other with the free arms. This has only been seen in some chimp populations, researchers said. The question remained whether chimpanzees are instinctively inclined to engage in grooming handclasps, or whether they learn it from each other and pass it on to subsequent generations. The researchers conducted observations between 2007 and 2012 at the Chimfunshi Wildlife Orphanage Trust in Zambia. At Chimfunshi, a mix of wild- and captive-born chimpanzees live in woodlands in some of the largest enclosures in the world. Previous research had suggested that the grooming handclasp might be a cultural phenomenon, just like humans across cultures engage in different ways of greeting each other. But this idea was mainly based on the observation that some chimp communities handclasp and others don’t – not whether there are differences between communities that engage in handclasping. Moreover, scientists said, the early observations could have been explained by different genetic and/or ecological factors among the chimp communities, rather than “cultural” differences. The new research suggests that even between chimp communities that engage in the grooming handclasp, subtle yet stable differences exist in the styles that they prefer. One group was found to prefer a style where they would grasp each other’s hands during the grooming, while another group preferred to fold the wrists around each other’s wrists. “We don’t know what mechanisms account for these differences,” said researcher Edwin van Leeuwen of the Max Planck Institute. “But our study at least reveals that these chimpanzee communities formed and maintained their own local grooming traditions over the last five 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 research team also observed that the grooming handclasp behaviour was a long-lasting part of the chimpanzees’ behavioural repertoire: the behaviour was even transmitted to the next generation of potential handclaspers. “By following the chimpanzees over time, we were able to show that 20 young chimpanzees gradually developed the handclasp behaviour 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 collaborator Mark Bodamer of Gonzaga University. “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,” van Leeuwen added.