Fair is Fine, but More is Better: Limits to Inequity Aversion in the Domestic Dog

Research with domestic dogs provides a unique approach for exploring the evolution of fairness and justice. Not only are dogs
descended from highly social canids; they have also been bred for cooperative tasks with humans. Dogs act cooperatively in
social play and are skilled on other social cognitive tasks. It is reasonable to ask whether dogs behave in ways similar to
primates in other social contexts. In particular, do dogs perceive and respond to unfairness or injustice, a skill potentially
borne of long-term affiliation with and selection by humans? Using a revised test of inequity aversion which looks at advantageous
and disadvantageous inequity, the current research investigated the behavior of 38 domestic dogs. Subject dogs and a control
dog approached two trainers in turn: one who rewarded them equally for sitting on command and one who rewarded them unequally—either
over-rewarding or under-rewarding the control dog. After familiarization with the trainers, subjects chose which trainer to
approach by themselves. Subjects preferred the over-rewarding trainer over the fair trainer; they had no preference between
the under-rewarding and the fair trainer. Further analyses found that length of ownership, subjects’ age, and cooperative
work experience reversed the approach preference, predicting preference for the fair trainer—though breed did not. These results
suggest that the precursory sensitivity, which dogs showed to iniquitous outcomes in prior research, does not extend to both
advantageous and disadvantageous inequity and does not hold when the subject is continually rewarded. Dogs selected a trainer
who had treated them “unfairly,” yet who presented a potentially greater opportunity for future rewards. When the stakes were
high, dogs showed a greater sensitivity to the quantity of a reward than to the fairness of a reward.