Ever feel like your dog was jealous when you played with another pooch? It might not have been your imagination, according to a new study.
The object of jealousy: a stuffed dog that barked and wagged its tail. Researchers compared how dogs reacted to their owners petting the faux canine with how they reacted to them showering love on a jack-o-lantern pail and reading a noise-making pop-up book aloud.
Dr. Christine Harris, an emotion researcher at UC San Diego, got the idea for the study after playing with her parents' three border collies.
"As I was petting the dogs, what happened is that one dog would push the other dogs head from out underneath my hand so that both hands were on him, and it wasn't just one dog who did this," she 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."
Harris adapted a study originally meant for six-month-old babies. When it was over, 72 percent of the dogs expressed jealous behavior (snapping at the object or pushing or touching the owner) when the fake canine was involved. Only 42 percent did the same with the pail and 22 percent with the book. One in four dogs actually showed aggressive behavior toward the fake dog, compared to only one dog out of the 36 in the study who snapped at the pail.
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That, according to the study, could be evidence of a "primordial form of jealousy" that could exist for a number of reasons. One possibility is that dogs developed jealous instincts as they evolved alongside humans and constantly vied with each other for food and attention.
"I think that it helps support the idea that we are not the only species that are wired to protect our bonded relationships from rivals," Harris said.
Stay! How to keep jealous behavior at bay
More studies have to be done before we can say definitively that dogs feel a basic form of jealousy. Packs are hierarchies, and what looks like jealousy could just be dominant dogs trying to assert themselves, Melissa Bain, associate professor of animal behavior at the UC Davis Veterinary Medical Teaching Hospital, told NBC News.
Whatever you call it, as a dog owner, a pushy pet can be really annoying.
"You need to set rules for interactions," Bain said. "If my son is yelling 'Mom, mom, mom!,' I'm not going to pay attention to him."
The trick is training the "jealous" dog not to shove its way in front of other dogs until it has obeyed a command, like sitting. (Note: This might not work as well for children).
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If the dog fails to perform the task, there is no need to punish it, Bain said. Just don't give it any attention. Eventually, it could learn to wait its turn before demanding a belly rub.
Sometimes, Bain said, dogs won't react well to being forced to wait, and could start acting up by hoarding resources and showing signs of aggression, like growling or snarling. That could be a sign of deeper hierarchical tensions and might require professional behavior training.
Not that Fido always minds being on the sidelines.
"It depends on the dog," Bain said. "Some don't care about attention as much as other dogs, so it might not be a big deal."
Keith Wagstaff writes about technology for NBC News. He previously covered technology for TIME's Techland and wrote about politics as a staff writer at TheWeek.com. You can follow him on Twitter at @kwagstaff and reach him by email at: Keith.Wagstaff@nbcuni.com