Evidence for Cultural Differences between Neighboring Chimpanzee Communities

Abstract

The majority of evidence for cultural behavior in animals has come from comparisons between populations separated by large geographical distances that often inhabit different environments. The difficulty of excluding ecological and genetic variation as potential explanations for observed behaviors has led some researchers to challenge the idea of animal culture. Chimpanzees (Pan troglodytes verus) in the Taï National Park, Côte d'Ivoire, crack Coula edulis nuts using stone and wooden hammers and tree root anvils. In this study, we compare for the first time hammer selection for nut cracking across three neighboring chimpanzee communities that live in the same forest habitat, which reduces the likelihood of ecological variation. Furthermore, the study communities experience frequent dispersal of females at maturity, which eliminates significant genetic variation. We compared key ecological factors, such as hammer availability and nut hardness, between the three neighboring communities and found striking differences in group-specific hammer selection among communities despite similar ecological conditions. Differences were found in the selection of hammer material and hammer size in response to changes in nut resistance over time. Our findings highlight the subtleties of cultural differences in wild chimpanzees and illustrate how cultural knowledge is able to shape behavior, creating differences among neighboring social groups.

Ecological and social correlates of chimpanzee tool use

“…We suggest that group members can gain important information about the characteristics of the tool site, tools required, techniques and outcomes from other tool users who act as tolerant or possibly even instructive models. This may serve to facilitate the acquisition of tool using skills and promote conformity in specific behavioural traditions within social groups [84] and populations [37,85]. Further, patterns of innovation (the successful diffusion or spread of an invention) are likely to drastically differ between tool using contexts.…”

Primate archaeology reveals cultural transmission in wild chimpanzees ( Pan troglodytes verus )

“…Long-term research of the Taï Chimpanzee Project has habituated three neighbouring study communities to the presence of humans (North, South and East Group). South Group, the community where the influx of immigration was observed, has been fully habituated since 2000 [42,50]. Based on the average home range size of our study communities according to group size, we estimated the potential home range of the SoS Group to have been approximately 36 km 2 [42,53].…”

“…Conformist transmission mechanisms in chimpanzees are supported by an increasing body of research that shows how conformity plays an important role in social learning strategies in a variety of wild ranging animal species [45][46][47]. Some studies have begun to thoroughly investigate how cultural transmission in wild chimpanzees may occur [42,48,49], yet how and why chimpanzees adopt certain behavioural traits and abandon their previous behaviour remain largely unknown [50,51]. With this study, we are aiming to investigate further whether immigrating females actively change their nut-cracking behaviour to match the tool selection of their new groups despite previously having acquired different preferences.…”

“…However, cultural differences between groups show that tool selection is flexible and influenced by group affiliation. We recently found variation in selected hammer materials between three neighbouring chimpanzee groups in the Taï National Park in Côte d'Ivoire despite similar ecological circumstances in their home range [42][43][44]. One community, the South Group, consistently used predominantly stone hammers to crack open Coula edulis nuts, while the two neighbouring communities, North and East Group, gradually increased the use of wooden hammers as the nut season advanced and nuts dried out and were easier to crack open.…”

“…They did not belong to one of the habituated communities and therefore no direct observation of their behaviour prior to their transfer was available. However, the following lines of argument provide supporting evidence that all these females originated from the chimpanzee community directly neighbouring the south of habituated South Group [42]. Longterm data of inter-group encounters of the Taï Chimpanzee Project reveal frequent encounters of the South Group with a large community in the south of their territory [51,53] (South of South, or SoS territory, figure 1).…”