Inequity aversion in dogs: a review

Jim Mcgetrick,Friederike Range

doi:10.3758/s13420-018-0338-x

Jim Mcgetrick, Friederike Range

Open Access

https://doi.org/10.3758/s13420-018-0338-x

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Abstract

The study of inequity aversion in animals debuted with a report of the behaviour in capuchin monkeys (Cebus apella). This report generated many debates following a number of criticisms. Ultimately, however, the finding stimulated widespread interest, and multiple studies have since attempted to demonstrate inequity aversion in various other non-human animal species, with many positive results in addition to many studies in which no response to inequity was found. Domestic dogs represent an interesting case as, unlike many primates, they do not respond negatively to inequity in reward quality but do, however, respond negatively to being unrewarded in the presence of a rewarded partner. Numerous studies have been published on inequity aversion in dogs in recent years. Combining three tasks and seven peer-reviewed publications, over 140 individual dogs have been tested in inequity experiments. Consequently, dogs are one of the best studied species in this field and could offer insights into inequity aversion in other non-human animal species. In this review, we summarise and critically evaluate the current evidence for inequity aversion in dogs. Additionally, we provide a comprehensive discussion of two understudied aspects of inequity aversion, the underlying mechanisms and the ultimate function, drawing on the latest findings on these topics in dogs while also placing these developments in the context of what is known, or thought to be the case, in other non-human animal species. Finally, we highlight gaps in our understanding of inequity aversion in dogs and thereby identify potential avenues for future research in this area.

Highlights

Inequity aversion refers to the resistance to inequitable outcomes and was initially proposed as an overarching explanation for seemingly contradictory behaviour of humans in economic experiments (Fehr & Schmidt, 1999)
The study of inequity aversion in non-human animal species has amassed a substantial body of work
Whether responses to inequity are based on simple physiological responses to being in the presence of a feeding partner or whether individuals perceive the inequity of the situation is not yet known

Summary

Introduction

Inequity aversion refers to the resistance to inequitable outcomes and was initially proposed as an overarching explanation for seemingly contradictory behaviour of humans in economic experiments (Fehr & Schmidt, 1999). If this latter hypothesis is true, it would suggest that the primitive form of inequity aversion shown in dogs was a false positive and that refusals to work in the RI condition were responses to the lack of reward This seems somewhat unlikely given the cases of quality inequity aversion already mentioned (Essler et al, 2017), the consequences of unequal rewarding on later social interactions (Brucks et al, 2016; see section on ultimate function, below), and the observation that even in the buzzer task of Brucks, MarshallPescini, et al (2017) pet dogs displayed more stress signals in the RI condition than the NR condition despite no difference in performance between these conditions. This recent and unexpected discrepancy across studies demands further investigation

Summary

Conclusion