Why intergroup variation matters for understanding behaviour

Abstract

Intergroup variation (IGV) refers to variation between different groups of the same species. While its existence in the behavioural realm has been expected and evidenced, the potential effects of IGV are rarely considered in studies that aim to shed light on the evolutionary origins of human socio-cognition, especially in our closest living relatives—the great apes. Here, by taking chimpanzees as a point of reference, we argue that (i) IGV could plausibly explain inconsistent research findings across numerous topics of inquiry (experimental/behavioural studies on chimpanzees), (ii) understanding the evolutionary origins of behaviour requires an accurate assessment of species' modes of behaving across different socio-ecological contexts, which necessitates a reliable estimation of variation across intraspecific groups, and (iii) IGV in the behavioural realm is increasingly likely to be expected owing to the progressive identification of non-human animal cultures. With these points, and by extrapolating from chimpanzees to generic guidelines, we aim to encourage researchers to explicitly consider IGV as an explanatory variable in future studies attempting to understand the socio-cognitive and evolutionary determinants of behaviour in group-living animals.

Chimpanzees behave prosocially in a group-specific manner

“…5C ), but also previously reported group-specific sociality [frequencies of close proximity and grooming: ( 26 )], mapped onto the differential expressions of prosociality across the studied chimpanzee communities. This pattern supports the posited importance of social tolerance in the expression of behaviors that facilitate group living ( 31 , 40 , 41 ) and warrants the expansion of the cultural differences approach in humans ( 42 , 43 ) to other animals, especially to species with social learning capacities ( 27 ). Evidence for the possibility of cultural transmission of prosocial behavior in chimpanzees was recently found in a prosocial choice task in which subjects exposed to generous conspecifics became more prosocial themselves ( 22 ).…”

“…especially to species with social learning capacities (27). Evidence for the possibility of cultural transmission of prosocial behavior in chimpanzees was recently found in a prosocial choice task in which subjects exposed to generous conspecifics became more prosocial themselves (22).…”

“…To capture natural social dynamics between chimpanzees, in this case, prosocial behavior, we propose to move the experimental paradigm from indoor testing with human-imposed selection of chimpanzee dyads to outdoor testing with free partner choice [also see (8,23,24)]. Moreover, on the basis of recent findings evidencing substantial variation in social dynamics across multiple groups of chimpanzees (25,26), we conjecture that the endeavor to investigate chimpanzee prosociality has been blind-sighted by single-group testing (27), with incongruent findings potentially attributable to intergroup differences between chimpanzee communities.…”

Group‐level variation in co‐feeding tolerance between two sanctuary‐housed communities of chimpanzees (Pan troglodytes)

“…More broadly, social tolerance is often seen as a facilitator for more specific behaviours with the potential to influence individuals' fitness, like social learning ( van Schaik, 2003), and collaboration or prosociality (Cronin, 2017;Horn et al, 2016;Yamamoto et al, 2009). Recently, an explicit appreciation for intraspecific (group-level) variation in social behaviour has emerged (e.g., Stevens et al, 2008;Schradin, 2013;van de Waal, 2018;Kaufhold & van Leeuwen, 2019).…”

Chimpanzees' behavioral flexibility, social tolerance, and use of tool-composites in a progressively challenging foraging problem

“…Many studies of behavioral flexibility in chimpanzees examine only one group of chimpanzees ( Bonnie et al., 2012 ; Manrique et al., 2013 ; Hopper et al., 2015a ). The findings of this study indicate that this approach may not lead to generalizable results, as the two groups in our study, despite sharing identical environments and similar rearing histories, performed quite differently (see Kaufhold and Van Leeuwen, 2019 ). Our examination of social interactions at the task highlights the fact that group-level, intraspecific differences in social tolerance may impact social behavior in a way that impacts performance on artificial tasks, particularly if these tasks are presented in group contexts (e.g., Lehner et al., 2011 ).…”