This article originally appeared on RealSimple.com.
We’ve long treated our dogs like humans, dressing them in sweaters, letting them sleep in our beds—even painting their nails. So it makes sense that we’re eager to attribute their canine behavior to human emotions, crediting a wagging tail to joy or lowered eyes to shame. Yet while research has shown dogs feel love and affection, more complicated emotions like embarrassment and guiltdon’t seem to be in their repertoire.
But here’s one that might be: Scientists at UC San Diego have found evidence suggesting that dogs could actually be capable of jealousy.
Although Charles Darwin wrote about dogs’ jealousy in 1871 and dog owners have been quick to offer anecdotal evidence ever since, there’s never been scientific proof of the phenomenon.
This experiment involved 36 dogs and their owners. The owners petted an animated toy dog while their real dog was in the room. They also petted and played with a jack-o-lantern, and sat reading a noise-making children’s book. Observers wrote down and cataloged the dogs’ reactions to each of these three situations, which ranged from biting, barking, and pushing at either the toy or the owner.
The dogs were more likely to show signs of aggression, attention-seeking behavior, and a heightened interest in their owners when the fake dog was the object of affection. Most of the dogs clearly thought the stuffed dog was real: 86 percent inspected and sniffed its butt at some point during the experiment.
“We can’t really speak to the dogs’ subjective experiences, of course,” study author and psychology professor Christine Harris said in a release. “But it looks as though they were motivated to protect an important social relationship.”
So is this behavior really the green-eyed monster as we know it? Not quite. Researchers called the envious emotion that dogs experience a “primordial” type of jealousy rather than the complicated thoughts that torment adult humans.
Infants show this instinctive kind of jealousy, too, when their mothers shower affection on another baby. The scientists behind the study say this could be evidence that jealousy is an innate emotion, like fear or anger, that humans share in common with other social creatures.
So if it seems like Fido is giving you the cold paw after you’ve shown some love to another dog, it might not be your imagination.