During my thesis, I have done extensive research on whether dogs and other animal species have a sense of morality. Since this topic is particularly close to my heart, I wanted to dedicate a separate article to this, though of course, I can only provide a short overview of comparative behavioral research on these pages.
My research was about finding out whether different animal species, including dogs, have feelings of justice or injustice. If so, they should prefer that rewards are being divided equally instead of one animal partner being favored over another, meaning the other receives a better or greater reward. In other studies, scientists have focused less on what animals chose and more on how animals respond to unfair treatment. The most famous example is probably the pioneering study by Brosnan and de Waal (2003). They rewarded one capuchin monkey with a piece of cucumber, while another capuchin monkey was given a piece of grape for the same task. The video of the monkey throwing in anger the cucumber at the experimenter (out of jealousy according to researchers) has already gone viral on YouTube. The scientists explain this observation as follows: They suspect that this so-called injustice aversion is an evolutionarily significant mechanism to encourage collaboration among social species by protecting individuals from being taken advantage of by others. (Brosnan, 2006; Brosnan & de Waal, 2014).
This assumption has certainly been questioned in the scientific world, at least because other research groups have not been able to establish the same results thus far (e.g., Dubreuil, 2006; Silberberg, 2009). To this day, there is a debate about what actually causes the behavior shown in the video. For example, feelings of frustration due to having received better rewards in the past (Roma et al., 2006) or the simple expectation of seeing a higher reward in front of you, independent from another individual, (Bräuer et al., 2006) have been suggested as alternatives to injustice aversion.
Regarding dogs, the research panorama is quite similar to the one in monkeys and other animal species.
Some studies could find evidence for inequity aversion (e.g., Range et al., 2009; Range et al. 2012; Brucks et al. 2016), but there are just as many that couldn’t (e.g., Brucks et al., 2017; Horowitz, 2012). So how should one imagine such an "experiment of justice" with dogs? One famous test involves two dogs sitting side by side and being asked to take turns giving the paw (e.g., Range et al., 2009). Different experimental conditions are being compared here: One in which the dogs receive different high/low-value rewards, another where they receive no reward at all, and a non-social condition in which only one dog is present. In such settings, some researchers were able to show that dogs, without being rewarded, stopped giving the paw sooner if another dog was sitting nearby and continued to receive cookies (Range et al., 2009). Another similar study used pushing a buzzer as a task (Essler et al., 2017).
But as I mentioned earlier, people are in disagreement on whether dogs have a sense of justice or not. I find this very interesting because I am sure most dog owners would be convinced that their dog is sensitive to injustice of any kind. Of course, Bello is definitely jealous, after all, he tries to push himself in and interrupt the situation when his owner pets another dog. He also wants to enjoy human attention just as much. Of course, Sunny thinks it’s unfair when Fipsi gets a delicious piece of sausage in front of her eyes and she doesn't get any. Her eyes really pop out with envy and she starts to whine desperately.
Well, if the facts are so undeniable, why go through the trouble and do scientific studies at all? And how is it, that some of these studies can't even find the most obvious?
Well, the problem with everyday observations is that they are not controlled situations, so it is hard for me to judge why my dog behaves a certain way. Humans are constantly interpreting our dogs' behavior in ways that seem logical to us. But it’s questionable whether what we interpret is actually what’s happening in our dogs. For example, Bello could push himself between his owner and another dog, just because he wants to keep the dog at a distance. Or in that moment he wants to be padded, independently of the other animal. Or he uses the situation to get closer to the other dog (at least that's my interpretation of Rico’s reaction when I pet an attractive female dog). And with Sunny, her endless passion for sausages could explain her behavior just as much.
Therefore, compared to everyday scenarios, in a scientifically controlled study, I can rule out any alternative explanations based on a controlled environment. We recall, for example, the non-social controlled condition in the Paws study where only one dog was present. Only this scenario allows me to look at how long my dog participates in the game (giving the paw) without receiving any reward at all, independent of another canine. Without this baseline, I simply cannot tell if the other dog has any influence at all by sitting next to my dog and continuing to receive rewards.
Hence, there is an almost infinite number of factors that additionally can change the behavior of an animal and, of course, that of a human.
Regarding injustice aversion animal studies have shown that for example, the relationship between two animals (e.g., Brosnan et al., 2005), the personality of the animals (Brosnan et al., 2015), or even the social hierarchy between two animals (e.g., Oberliessen et al., 2016) influence the extent to which they react to injustice or try to avoid it (this does not apply to all cases, of course).
Aside from what appears to be a number of very plausible influencing variables, some are simply puzzling and cause sleepless nights to one or the other behavioral scientist. For example, it seems to make a difference in dogs whether the rewards they receive come from the same food bowl or two different food bowls. With one bowl, the dogs responded aversively to unfairness; with two bowls, they did not (cf. Brucks et al., 2017). You see, the devil really is in the detail here!
On that note, it isn’t surprising that research on animals' perception of injustice is far from complete. I, too, can confirm according to my own experience that every new test raises at least as many questions as it gives answers.
At the same time, it is of course incredibly exciting and, in my eyes, also very important to gain an even better and deeper understanding of how our four-legged friends actually think and feel.