A paper which is getting frequently linked to across social media platforms lately has been this study which argues that alongside humans (and human infants) dogs are capable of feeling jealousy.
In my small circle of aquaintances, the overwhelming response of those with a pooch is one of "well duh...". Initially, I felt myself agreeing with them, before I took a step back and tried to cleanse myself of the urge to anthropomorphise. Although it would be lovely to think that dogs were capable of the same complex emotional ability as we are, upon further contemplation I feel a little uncertain about the conclusions drawn in it.
I would argue the aggression stems from insecurity at feeling demoted in a pack situation because the pack leader (owner) is giving attention to and thereby promoting another individual/object. That is a far more primitive instinct and is different from feeling jealousy i.e. envious resentment. The dogs don't feel envious of the object receiving attention, they feel threatened by it. I’d argue that’s backed up by the fact that in most cases the dogs reacted aggressively or dominantly (to assert their position in the pack), whereas the emotional jealousy familiar to us doesn’t need to be (and often isn’t) acted upon.
I'm not sure whether the distinction is purely semantics, but my instinct is that human jealousy is a far more complex cognitive emotion than what is at the root of the behaviours shown in this study. Is it possible that we're guilty of anthropomorphising our pets, to save the dent to our egos if we knew that they don't love us in the same way that we love them?