Humans may not be the only animals to experience jealousy. A new study published in the online scientific journal PLOS ONE lends support to the theory that dogs get jealous too.
The idea for the research came when a University of California, San Diego psychology professor saw her family's border collies exhibit some intriguing behavior.
"As I was petting the dogs, what happened is that one dog would push the other dog's head from out underneath my hand so that both hands were on him, and it wasn't just one dog who did this," Dr. Christine Harris told NBC News. "They were not content to be sharing attention and resources. There was something about this exclusivity that made me think I was seeing a basic jealous behavior."
To conduct the study, Harris adapted a model used in studies designed to analyze emotion in infants. Thirty-six dogs were observed as their owners ignored them and focused their attention instead upon either a realistic stuffed dog, a plastic jack-o'-lantern pail or a children's pop-up book. The dogs were then evaluated for aggressiveness, attention-seeking behavior and interest in the owner and object.
The dogs showed more interest in the faux dog, which could bark and wag its tail, than in the pail or book. All of the dogs nudged their owners when they played with the stuffed animal, and 86 percent tried to push the fake dog during that stage of interaction.
The authors write:
We found that dogs exhibited significantly more jealous behaviors (e.g., snapping, getting between the owner and object, pushing/touching the object/owner) when their owners displayed affectionate behaviors towards what appeared to be another dog as compared to nonsocial objects. These results lend support to the hypothesis that jealousy has some "primordial" form that exists in human infants and in at least one other social species besides humans.
Since most of the dogs sniffed the behind of the stuffed toy, researchers surmised that the dogs may have believed the toy to be real. And given that the pets reacted so strongly to a fake dog, they concluded that the data present a "strong case that domestic dogs have a form of jealousy." This "primordial" form of the emotion is theorized to occur without complex cognition -- meaning a dog does not have to reflect on itself to experience the emotion.
"Many people have assumed that jealousy is a social construction of human beings -- or that it's an emotion specifically tied to sexual and romantic relationships," Harris said in a written statement. "Our results challenge these ideas, showing that animals besides ourselves display strong distress whenever a rival usurps a loved one's affection."
The study isn't the first evidence suggesting that animals experience jealousy or other emotions. Primates are widely believed to experience jealousy, and previous research suggests that dogs and horses do too.
The most recent study does not prove that dogs feel jealousy (though it's not a novel concept that dogs process emotions like humans). But if subsequent research does show that dogs are capable of feeling jealousy just like humans, it would certainly say a lot about the emotion.
As Laurie Santos, director of the Canine Cognition Center at Yale University (who did not work on the study), told NPR, "[E]ither jealousy is less complicated because animals show it, or animals are more complicated than we thought."
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