Researchers from UCSD have discovered that dogs can, in fact, experience a very basic form of jealousy.

The findings suggest that emotions as we understand them may have very ancient and primal origins.

“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,” said UC San Diego psychology professor Christine Harris. “Our results challenge these ideas, showing that animals besides ourselves display strong distress whenever a rival usurps a loved one’s affection.”

That’s really what they believe jealousy is all about for animals – it’s a response to the possibility that an intruder might be a threat to established social bonds, which require significant investment in terms of time and emotion.

For the study, they modified an experiment initially intended to gauge jealousy in human babies: Dog owners were placed in a room with their dogs and asked to ignore them in favor of either a plastic pail, a pop-up book, or a stuffed dog that barked and wagged its tail. In the cases of the pail and stuffed dog, they were asked to treat the object as a real dog, speaking softly and petting it (the book contained melodies to produce a similar effect).

Overwhelmingly, dogs were found to nudge, snap or otherwise intervene when their owners interacted with the stuffed dog. The researchers found they believed the toy god to be real, with nearly 90% of dogs attempting to sniff its rear end. The findings are pretty clear: When a dog believes its owners affection is being diverted to a rival dog, they dislike the feeling and will act out.

“Our study suggests not only that dogs do engage in what appear to be jealous behaviors but also that they were seeking to break up the connection between the owner and a seeming rival,” Harris said. “We can’t really speak to the dogs’ subjective experiences, of course, but it looks as though they were motivated to protect an important social relationship.”

The full study can be found in the journal PLOS ONE.