Scientific Evidence That Your Dog Gets Jealous

Any dog owner who has spent a weekend caring for a friend's dog will know this to be true, but scientists have shown it to be so: Your dog gets jealous when you play with other dogs.

Dog jealousy is something that you've probably seen often. Its origins date back to Charles Darwin, who once wrote that "everyone has seen how jealous a dog is of his master's affection, if lavished on any other creature. This shows that animals not only love, but have desire to be loved."

Well, despite all the anecdotal evidence we've seen throughout the annals of history, there was no experimental evidence to show this was true. Now, we have it. In a new study published in PLOS ONE, researchers found that dogs get jealous when their owners play with some strange dog.

Or, in this case, a stand-in for a strange dog. Christine Harris and Caroline Prouvost of the University of California San Diego modified an experiment used to test infants for jealousy (in that one, mothers played with a doll).

Here, 36 dog owners were locked in a room with their dogs and were asked to pet a stuffed dog (albeit one that "barked, whined, and wagged its tail when a button on the top of its head was pressed") and ignore their own dog. Then, the owners were asked to show the same amount of affection to a jack-o-lantern, to see if dogs were pissed about their owners showing affection to anything or just didn't want some four-legged stuffed jerk dog getting all the attention.

Turns out, when owners petted the stuffed dog, their actual dogs were more aggressive, raised their tail up, tried to push their way in between the stuffed dog and their owner, and barked. When the same attention was lavished on a jack-o-lantern, the dogs didn't care as much. The dogs also didn't care so much when a children's book was made to play noises (as sort of a test case to see whether the dogs were merely responding to the noise the stuffed dogs made).

Growing up, my dogs always got jealous when my mom showed me any affection—I'm not a dog, and I'm not a jack-o-lantern, so what's the deal? I guess that's for another study.

The jealousy that dogs feel and the jealousy that humans feel are probably different, with dogs obviously feeling a more basic sense of the emotion.

"The current findings add support to the emerging view that there is a primordial form of jealousy," Harris wrote.

That raises the question: Why do dogs feel jealousy? Harris has a few theories. Jealousy could be an old trait seen in many types of social animals, particularly ones that raise multiple young at the same time. The thinking goes that a more jealous puppy will, overall, get more food when it's being raised and thus be fitter to live to adulthood. They could have evolved jealousy just like we did—as a defense mechanism to sexual interlopers or as a way of being cautious against rival packs of dogs (or, in our case, people).

But, perhaps most interestingly, Harris theorizes that dogs may have evolved to be jealous as they were being domesticated and learned to rely on humans to survive.

"One might speculate that even if several social species have the capacity for jealousy, dogs may be the only species besides humans in which the emotion can be evoked in connection with a member of a different species," she wrote. "Perhaps this is a function of their emotional bonding with humans along with their motivation and ability to track human gaze/attention. Humans, after all, have been rich resource providers over our evolution."

So, yet another reason why humans and dogs get along so great—we both get jealous every now and then, so go ahead and empathize with your dog next time it gets a little green.