It seems that every year we get more data indicating the similarity between the emotional and mental life of human children and that of dogs. The issue of emotions in dogs is a very controversial one although there is some consensus that the range of emotions experienced by canines is similar to that experienced by human children between the age of two and three years (click here for more on this). However, looking at the available research, except for the issues of anger and aggression, it appears that scientists have not spent a lot of effort studying the emotions in dogs that we tend to consider to be negative or less than desirable. Such issues are important, however scientists, like pet owners, seem to have a bias toward concentrating on topics that might cast their dogs in a positive rather than a negative light.
However some negative emotions are extremely important and are certainly worthy of research. Take the issue of jealousy. In humans this is an important emotion since it has been found to be the third leading cause of non-accidental homicides worldwide. The defining feature for jealousy is a social triangle which arises when there is an important relationship between two individuals and a third individual intervenes to try to co-opt the affections or favors from one of the original pair, thus shutting out the remaining person. Some researchers feel that jealousy is a very primitive emotion which really does not take much deep thought. They believe that jealousy can be triggered by the relatively simple perception that a loved one's attention has been captured by a potential usurper. This seems to be confirmed by the fact that several studies have found that jealousy can appear in human infants as young as six months of age. In these studies the infants showed jealousy when their mothers interacted with what appeared to be another infant (but was actually just a realistic looking doll), but not when the mother interacted with something which was a clearly inanimate object.
Since the mental life of dogs involves emotions which are much more complex than that of a six-month-old child it seems to be sensible to propose that dogs may also feel jealousy. Prior to now there has been only one other study which looked at this issue (click here to read about that), however some scientists feel that that particular piece of research was really looking at the issue of a dog's perception of fairness and that the emotion involved could be envy rather than jealousy. Some new data, however, uses a variation of the same research design that was used to test for jealousy in children and it seems to have come up with an unambiguous answer. This research was done by Christine Harris and Caroline Prouvost of the University of California San Diego and it was published in the journal PLoS ONE*.
The setup of this experiment was quite straightforward and 36 dogs were tested. The jealousy condition involved a realistic looking stuffed mechanical dog that barked and wagged its tail as if it were real dog. The dogs tested in the experiment clearly suspected that the toy might be a real dog since 86% of them sniffed the anal region of this simulated dog during the test or afterwards (in the same way that they might have sniffed at an unfamiliar real dog).
In the jealousy condition the dog's owner interacted with the toy dog as if it were an actual dog by petting it, talking sweetly, and so forth. In another condition the owners engaged in exactly the same behaviors but did so towards something which was obviously not alive (a jack-o'-lantern shaped plastic pail). This was done so that the researchers could see whether it was just the affectionate behaviors being directed something other than the pet dog that was enough to trigger jealous behaviors. Finally in the third condition the owner read aloud from a children's book which had pop-up pages and played melodies. This condition allowed the researchers to test whether the dog's behaviors were really associated with jealousy or was just due to the fact that the owner was no longer paying attention to their pet.
The interactions were videotaped and analyzed later to measure specific signs of jealousy. These signs included aggression, attention seeking, attempts to break up the interaction, and how interest and attention were directed. The results were quite unambiguous. In terms of aggression, one fourth of the dogs snapped at the toy dog when their owner was playing with it. It was clearly a seething aggression caused by the jealousy since after the owner put the toy dog down at the end of the test period, 36% of the dogs snapped at the toy dog when the opportunity arose. Such snapping behavior in the other conditions was confined to just one dog. In terms of attention seeking and disrupting the interaction every single dog pushed at its owner to try to get his or her attention when they were playing with the toy dog and 87% of them pushed at the fake dog. This pushing behavior was extremely rare in the other conditions.
So this data makes it quite clear that dogs do appear to feel jealousy and respond to it in much the same way that human children do. As we learn more about dogs it appears that we are also learning that their mental lives are more complex than we suspected. Not only do dogs feel love (for example click here) but also some not so noble feelings, like jealousy and envy, much the same way that we do. Dogs are not angels, nor are they devils, but rather, like people, they are multifaceted, and like young humans they experience a broad range of positive and negative emotions.
Stanley Coren is the author of many books including: The Wisdom of Dogs; Do Dogs Dream? Born to Bark; The Modern Dog; Why Do Dogs Have Wet Noses? The Pawprints of History; How Dogs Think; How To Speak Dog; Why We Love the Dogs We Do; What Do Dogs Know? The Intelligence of Dogs; Why Does My Dog Act That Way? Understanding Dogs for Dummies; Sleep Thieves; The Left-hander Syndrome
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* Harris CR, Prouvost C (2014) Jealousy in Dogs. PLoS ONE 9(7): e94597. doi:10.1371/journal.pone.0094597