Inequity aversion in dogs: a review

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.

Do guide dogs have culture? The case of indirect social learning

“…It is, in fact, this whole system that is being conditioned in the classical experiment (Lorenz, quoted in Jenkins et al, 1978; on dogs' exhibition of social behaviours during conditioning experiments, see also Miklósi, 2014, p. 5). Some canine ethologists even suggest that the reward, which plays a key role in conditioning (training), can provoke a form of "aversion for lack of equity" in dogs (McGetrick and Range, 2018).…”

Social and Non-social Mechanisms of Inequity Aversion in Non-human Animals

“…As a consequence, the disadvantaged monkey refused to exchange the token, or rejected the cucumber reward entirely, tentatively reminiscent of the behavior of human responders in the impunity game (see below for critical discussion). Since this early study, IA was replicated in capuchin monkeys (van Wolkenten et al, 2007; Fletcher, 2008; Takimoto et al, 2010; Takimoto and Fujita, 2011), and reported in macaques (Massen et al, 2012; Hopper et al, 2013), chimpanzees (Brosnan et al, 2005, 2010), cotton top tamarins (Neiworth et al, 2009), dogs (Range et al, 2009, 2012; Brucks et al, 2016; see McGetrick and Range, 2018 for an overview), wolves (Essler et al, 2017), crows (Wascher and Bugnyar, 2013), rabbits (Heidary et al, 2008) and rats (Oberliessen et al, 2016).…”

No evidence for a relationship between breed cooperativeness and inequity aversion in dogs

“…Many non-human animal species compare payoffs with social partners and display negative responses to inequity (see Brosnan [1], Brosnan and de Waal [2], McGetrick and Range [3], and Oberliessen and Kalenscher [4] for review). Such inequity aversion is thought to counteract exploitation and, consequently, to contribute to the maintenance of cooperation [5][6][7], particularly among non-kin.…”

“…Domestic dogs represent a useful model species to further explore the link between inequity aversion and cooperation. Domestic dogs were the first non-primate species found to exhibit inequity aversion and are now one of the best studied species in this field (see McGetrick and Range [3] for review). Range et al [65] reported that when subjects were asked to give their paw in an inequity task (the "paw task"), they stopped complying sooner, and hesitated longer, if their partner received a reward and they themselves did not, compared with the equity condition in which both dogs received an equal reward for the same task.…”

“…Although this result provides evidence that the cooperativeness of the dog breed may be positively correlated with an aversion to inequity, this difference between the breed groups was not statistically significant. More importantly, however, it is questionable whether the experiment actually assessed inequity aversion (see Horowitz [69] and McGetrick and Range [3] for discussion). Thus, it remains to be seen whether cooperative and independent worker breeds truly differ in the extent to which they are inequity averse.…”