Anyone with two dogs will probably tell you that dogs definitely feel jealousy. Is it true? Will it be harmful for the dog's owner?
There is no way to answer questions about what dogs do and don't feel since we can't ask them like we can ask humans. What we know about dog emotions comes from brain scans and mapping. For example, we know that when dogs see or hear their owners, their brains light up in the same places that human brains do when they see people they love. So we say that dogs "love" us, although that emotion is likely quite a bit different from the way humans experience love.
(Side note: Jealousy is an interesting emotion in humans because it's not really a true emotion at all. Instead, most people experience it as a side effect of fear, anxiety, insecurity, or unfulfilled desire. If you haven't thought about that idea before, it might take some time to sink in, but I bet that if you think back to times you've been jealous, you can deconstruct that feeling into some combination of those other emotions.)
Anyway, so no one knows if dogs feel something like what humans describe as "jealousy." We do know that some dogs will present certain behaviors in situations where a human might feel jealous, such as:
- jumping or barking at two humans hugging or cuddling
- offering a toy when humans are not paying attention to it
- barking, lunging, or offering a toy when other dogs are playing
Dogs request human attention in a variety of ways. You can call it jealousy if you want, or you can call it something else.
It is worth noting that sometimes behavior is ascribed to "oh, my dog is just jealous" when the dog is not seeking attention at all but is anxious or nervous with the situation.
For example, in the first case that I mentioned above, where a dog barks when her owner hugs another human. The dog might be seeking attention but might also be nervous that the other human could hurt her owner. This sort of behavior is frequently presented by dogs that have seen domestic abuse, although it is also done by dogs who have only seen healthy human relationships (so don't assume that the owner was or is being abused).
In most cases, behavior that is listed as "jealous" is not an issue for dog owners. It might be mildly annoying at worst. However, in some cases, it can get out of hand. A dog that brings a toy and tries to play when the humans are busy eating dinner is easy to ignore until the dog starts barking incessantly or jumps on the table.
Have I fully answered your question? I hope this helps!
There actually is absolute, quantitave proof that dogs get jealous. It is not just personification. Emotions are certain chemicals that are electrically stimulated and then are fired across these "arms" of our brain cells which are called axons and dendrites. As the ends of the dendrites receive this stimulation, and this is all that feelings are. With MRI's we can see where this occurs in the brain and by how much. We also have confirmed that those exact same chemicals which are the ones responsible for emotion do exist in dogs through examination of cerebral spinal fluid
By putting dogs in MRI machines, we then proved, they do actually love us. They also confirmed that they feel joy, hate/anger (biochemically they're the same), fear, and loss. Also, they did studies with dogs where they compared them with toddlers. The behaviors were identical, and observation is the first step in the scientific method. Whether it's the behavior of two substances in a chemical reaction, or the behaviors of two different microorganisms together, or a comparative study between human three-year-olds.