Date Published: May 1, 2019
Publisher: Public Library of Science
Author(s): Rachel Dale, Sylvain Palma-Jacinto, Sarah Marshall-Pescini, Friederike Range, Elsa Addessi.
Prosociality is important for initiating cooperation. Interestingly, while wolves rely heavily on cooperation, dogs’ do so substantially less thus leading to the prediction that wolves are more prosocial than dogs. However, domestication hypotheses suggest dogs have been selected for higher cooperation, leading to the opposing prediction- increased prosocial tendencies in dogs. To tease apart these hypotheses we adapted a paradigm previously used with pet dogs to directly compare dogs and wolves. In a prosocial choice task, wolves acted prosocially to in-group partners; providing significantly more food to a pack-member compared to a control where the partner had no access to the food. Dogs did not. Additionally, wolves did not show a prosocial response to non-pack members, in line with previous research that social relationships are important for prosociality. In sum, when kept in the same conditions, wolves are more prosocial than their domestic counterpart, further supporting suggestions that reliance on cooperation is a driving force for prosocial attitudes.
Humans show wide-ranging and regular prosociality (i.e. a voluntary action which benefits another) [2,3], however phylogenetic relatedness to humans does not seem to explain the extent of prosociality other species show [4–6]. While chimpanzees show prosocial responses in some tasks [7–9], in many they do not [4,10–12], whereas some more distantly related monkey species show more consistent prosociality [6,13–17]. Therefore, recent studies have taken more of a comparative approach to consider possible convergent selection pressures that may be at play. In line with this approach, pet dogs have been considered as a good model as they are not closely related to humans but share the same environment . Indeed it has recently been found that pet dogs do show prosociality towards familiar conspecific partners in a simplified prosocial choice task, where they could choose for how many trials to continue delivering a reward to a partner [19,20]. Some domestication hypotheses suggest that dogs have been selected for higher tolerance and cooperation , thus predicting that dogs should show prosocial tendencies. Therefore these findings may suggest that prosocial tendencies could have appeared during the course of domestication, meaning that their social proximity to humans drove the evolution of more prosocial behaviour.
A generalized linear mixed model (GLMM) revealed an interaction between species and condition on the number of trials in which the giving symbol was chosen (χ2 = 13.53, df = 4, p = 0.009), therefore each species was considered separately.
In a directly comparable set-up, we detected prosocial responses in wolves, but not dogs, in an experimental prosocial choice task. Our results support the predictions of the ‘socio-ecology’ and ‘cooperative breeding’ hypotheses , that the reliance on cooperation in wolves has shaped other aspects of their behaviour, including prosocial regard. The fact that wolves, but not dogs, were prosocial in the same task corroborates other findings that wolves are more tolerant with food sharing, a naturalistic measure of prosociality, than dogs . Furthermore, wolves have been shown to be far more successful in experimental cooperation tasks than dogs , and are more sensitive to unequal reward distributions . Wolves extensively rely on cooperation for many aspects of their lives including breeding , hunting  and territory defence . Dogs, on the other hand, cooperate less than wolves in free-ranging settings, usually foraging solitarily and raising offspring alone . The current study therefore further strengthens the suggestion that prosocial behaviour is an important factor for cooperative species, and taken together these experiments support a broader link between cooperation, prosociality and inequity aversion [6,39,40].