A new study by researchers at the University of California San Diego suggests that dogs may experience jealousy toward other dogs. It is the first experimental test of this behavior in dogs and casts doubt on the idea that jealousy is purely human or a social construct.

The research, published in the journal PLOS ONE by UC San Diego psychology professor Christine Harris and former honors student Caroline Prouvost, examined canine behavior when confronted with a potential rival.

The researchers videotaped 36 volunteer dog owners who were given three objects to interact with, in their own homes. The owners were asked to interact with a jack-o-lantern pail and a stuffed dog that barked, whined and wagged its tail as if they were dogs. They were also asked to read a interactive pop-up book that played music.

The results showed that dogs were more likely to exhibit jealous behavior toward the imitation dog than either of the other two objects.

When owners interacted with the stuffed dog, 78 percent of dogs pushed or touched their owners and 30 percent of them tried to get between the owner and the imitation dog and 25 percent snapped at it.

When the owners interacted with the jack-o-lantern, only 42 percent of the dogs became upset and 22 percent were bothered by the book. Only one dog snapped at the plastic pumpkin and the book.

“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. 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,” said Harris in a statement.

The researchers believe, based on the dogs behavior, that they considered the stuffed dog to be a legitimate rival. Not only was the dogs behavior aggressive, but 86 percent of them sniffed the toy’s rear end.

The majority of research on jealousy focuses on human subjects, including mates, siblings, friends and co-worers. The behavior has been observed in babies and young children. It is known to have a profound influence on human relationships and society but has generally been thought to be exclusive to humans.

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