Efficient social learning plays an essential role in human life as it provides the basis for traditions and culture (Plotkin 2007
). As a consequence, studying the roots of culture in other animals has been a key research topic for decades (Whiten 2009
). Theoretical studies on social learning rules suggest that individuals should be selective when deciding both when to learn socially and who to choose as a model (Boyd & Richerson 1985
; de Waal 2001
; Henrich & Gil-White 2001
; Giraldeau et al. 2002
; Laland 2004
; Mesoudi 2008
). A few empirical studies have identified rules for choosing models (Nicol & Pope 1999
; Schwab et al. 2008
), revealing typically that successful individuals are likely to induce social learning. For example, laboratory experiments demonstrated that nine-spined sticklebacks preferably copied foraging patches of larger individuals (Duffy et al. 2009
). However, sticklebacks are also able to compare their own foraging success with the success of others and choose foraging locations accordingly (Kendal et al. 2009
). This latter result implies that these fish are flexible with respect to the question ‘who is a good model?’ and are thus able to choose the best option in each situation.
For primates, living in stable social groups with hierarchical structures and certain levels of kin relationships (Smuts et al. 1987
), it has been argued that certain individuals are predisposed to be models for other group members, independent of their suitability in a given situation (de Waal 2001
). The ‘social model hypothesis’—also known as bonding and identification-based observational learning (BIOL)—predicts that primates living in structured social groups are most likely to learn from social models such as knowledgeable, older, high ranking members of the same group and species (de Waal 2001
). In addition, the hypothesis predicts that social learning in this taxonomic group is linked to conformity. Young and subordinate individuals want to behave like old and dominant individuals do. Therefore, individuals may copy the behaviour of models even if their behaviour is unsuitable for the current situation, and fail to copy the behaviour of other group members even when that would be favourable (de Waal 2001
). The hypothesis could explain why the use of humans as models often yields negative results for social learning in non-human primates, despite the models' perfect knowledge for the tasks in question (Call & Tomasello 1996
). In contrast, the use of female conspecifics as models has allowed the demonstration of the development of arbitrary traditions in captive chimpanzees (Whiten et al. 2005
). Nevertheless, there are no demonstrations that an individual's identity (that is, its relatedness to other group members and/or its social status) affects the likelihood that others will copy its behaviour.
In this paper we report tests of the social model hypothesis in a field experiment on six vervet monkey groups. We used a standard experimental design in laboratory studies on primates: a baited box, called an ‘artificial fruit’ (Whiten et al. 1996
). These artificial fruits can be opened in two different ways, but one option is blocked during the demonstration phase so that models consistently open the box in one way (). During the experiment, subjects could potentially open the box in both ways. Therefore, a significant repetition of the models' behaviour demonstrates social learning. We had three groups where the dominant female acted as model and three groups where a dominant male acted as model. In vervet monkeys, females are the philopatric sex, while males migrate at sexual maturity (Dunbar & Thelma 2001
). Therefore, we could investigate a more refined aspect of the social model hypothesis, namely that members of the philopatric sex might elicit more social learning than members of the migrating sex. In that case, we predicted that female models would be more likely to attract group members to the task and more likely to induce social learning than male models. In contrast, if dominance per se
is a key factor to induce social learning, we predicted that groups with male models would learn as well as groups with female models.
(a) A vervet monkey manipulating the pull door, marked with wooden colour, and (b) a vervet monkey manipulating the slide door, marked with black colour.
In our experiment, any effect of the sex of the model on the likelihood of social learning could not be explained by differences in relevant knowledge, but two alternative explanations would remain. First, members of one sex could be more aggressive, keeping group members away and therefore precluding efficient social learning. Second, group members might pay selectively more attention to the actions of models of one sex, therefore being more likely to learn from members of this sex. To distinguish between these alternatives, we noted the number of bystanders during the demonstrations, whether they looked at the model during the moment of box opening and the number of aggressive actions initiated by the model during the demonstrations. We predicted that if tolerance is the key to successful social learning, models of the less aggressive sex would elicit a greater number of bystanders. Likewise, we predicted that if the effect of the sex of the model is caused by selective attention, models of the sex that elicits more successful social learning would receive more attention during the task.