Food cleaning in gorillas: Social learning is a possibility but not a necessity

Abstract

Food cleaning is widespread in the animal kingdom, and a recent report confirmed that (amongst other behaviours) wild western lowland gorillas also show food cleaning. The authors of this report conclude that this behaviour, based on its distribution patterns, constitutes a potential candidate for culture. While different conceptualisations of culture exist, some more and some less reliant on behavioural form copying, all of them assign a special role to social learning processes in explaining potentially cultural behaviours. Here we report the results of an experiment that tested to what extent food cleaning behaviour in a group of captive Western lowland gorillas (Gorilla gorilla gorilla) relies on social learning processes. Subjects were provided with clean and dirty apples. When they were provided with dirty apples, all subjects showed evidence of food cleaning in at least 75% of trials. Preferred cleaning techniques differed between individuals, four out of five of subjects expressed a behaviour analogous to that reported in wild conspecifics. Given this occurrence of food cleaning in a culturally unconnected population of gorillas, we conclude that social learning is unlikely to play a central role in the emergence of the food cleaning behavioural form in Western lowland gorillas; instead, placing a greater emphasis on individual learning of food cleaning’s behavioural form.

Naïve orangutans (Pongo abelii & Pongo pygmaeus) individually acquire nut-cracking using hammer tools

“…Importantly, the ape ZLS hypothesis predicts successful reinnovation of behavioural forms by naïve ape subjects provided the right conditions and in the absence of any copying opportunities. This prediction holds true in a fast-growing experimental literature detailing successful individual acquisitions of various wild-type behavioural forms (including tool use) across various species of naïve, captive great apes (Allritz, Tennie, & Call, 2013; Bandini & Tennie, 2017; 2019; Bandini & Harrison, in press; Menzel, Fowler, Tennie, & Call, 2013; Neadle, Allritz, & Tennie, 2017; Tennie, Hedwig, Call, & Tomasello, 2008). Therefore, the ape ZLS hypothesis has growing support, but whether it can also explain the behavioural form of nut-cracking is still an open question.…”

“…Thus, this study adds another behaviour to the growing list of primate tool-use and social behavioural forms that have been found to be culture- in dependent forms (the authors are very grateful to C. Schuppli for suggesting this term), i.e. latent solutions (e.g., Allritz et al, 2013; Bandini & Tennie, 2017; 2019; Menzel et al, 2013; Neadle et al, 2017; Reindl & Tennie, 2018; Tennie et al, 2008). Although this study did not find evidence for (non-copying) social learning increasing the frequency of target behaviour (as the older orangutans may have been fixed in their alternative, successful method of cracking open the nuts with their teeth), it is likely that, similar to other ape behaviours, non-copying variants of social learning can increase and stabilise the frequency of nut-cracking within populations – at least when these mechanisms apply across generations (see also discussion in Moore, 2013).…”

“…That is, according to the ZLS account, social learning plays a role (even a large role) but copying variants of social learning are excluded, which is justified by the absence of evidence for spontaneous copying in apes (see above). Given that (non-copying) social learning plays some role, the affected ape behaviours are only cultural in a minimal sense of the word (see Neadle, Allritz, & Tennie, 2017). Importantly, the ape ZLS hypothesis predicts successful reinnovation of behavioural forms by naïve ape subjects provided the right conditions and in the absence of any copying opportunities.…”

“…Past LS studies have demonstrated that multiple target behavioural forms – including tool use behavioural forms – can be individually acquired by primates (see above). Furthermore, it was also shown that different species may sometimes overlap in their latent solution repertoires (Allritz et al, 2013; Bandini & Tennie, 2019, 2017; Menzel et al, 2013; Neadle et al, 2017; Reindl, Beck, Apperly, & Tennie, 2016; Tennie et al, 2008).…”

Ape cultures do not require behaviour copying

“…Given certain combinations of parameters, such as higher genetic and ecological diversities, the same population level pattern can be obtained even when reinnovation is not socially mediated, i.e if oranzees are not influenced by the behaviors of the other individuals in their populations. That is, similar patterns can exist when the underpinning individual-level mechanisms are not cultural even in a minimal way (Neadle, Allritz, and Tennie 2017). However, socially mediated reinnovation is likely required to explain observed differences in behavioral frequencies between the subset of ape populations that exist in genetic contact and that share similar environments (Langergraber et al 2011).…”