Even though some scientists have argued that jealousy is an entirely social construct, dog owners would not dispute that their puppies can be as possessive as humans and the first ever experiment on dog jealousy only confirms this.
"Our study suggests not only that dogs do engage in what appear to be jealous behaviour but also that they were seeking to break up the connection between the owner and a seeming rival," said Christine Harris, a professor of psychology at University of California, San Diego in the US.
"We can not really speak to the dogs' subjective experiences, of course, but it looks as though they were motivated to protect an important social relationship," Harris added.
The findings support the view that there may be a more basic form of jealousy, which evolved to protect social bonds from interlopers.
Dogs exhibit more jealous behaviours, like snapping and pushing at their owner or the rival, when the owner showed affection to what appeared to be another dog, showed the findings.
For the study, the researchers adapted a test used with six-month-old human infants.
They worked with 36 dogs in their own homes and videotaped the owners ignoring them in favour of a stuffed, animated dog or a jack-o-lantern pail.
Dogs were about twice as likely to push or touch the owner when the owner was interacting with the faux dog (78 percent) as when the owner was attending to the pail (42 percent). Even fewer (22 percent) did this in the book condition.
About 30 percent of the dogs also tried to get between their owner and the stuffed animal.
And while 25 percent snapped at the "other dog," only one did so at the pail and book.
The study appeared in the journal PLOS ONE.