Scientists at the University of California at San Diego confirmed their hypothesis by studying a number of dogs and analyzing the way each reacted when their owners displayed affection toward inanimate objects.
When owners were visibly loving and affectionate toward a dog-like stuffed animal (that barked, whined and wagged a mechanized tail), the majority of real dogs showed aggression toward their perceived rivals. When owners were similarly demonstrative toward a more obviously inanimate object -- a bucket or pail, in this instance -- only a handful of dogs seemed to pay any mind.
In the study, published this week in the journal PLOS ONE, lead author and San Diego psychology professor Christine Harris concluded the results suggest dogs get jealous just like humans.
Harris's research was assisted by honors student Caroline Prouvost.
"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 study builds on previous research that shows even infants began displaying jealous behaviors.
"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," Harris said. "Our results challenge these ideas, showing that animals besides ourselves display strong distress whenever a rival usurps a loved one's affection."