Any behavior has both genetic and learned components. The genetics operating in this case may be those governing willfulness (dominance," if you will) and prey drive (modified by us humans to facilitate their prior use for herding cattle). The learning, or nurtural components, in this case could be positive or negative reinforcement.
Let us suppose, for a moment, that your dog is displaying the behavior because of dominance with negative reinforcement of the behavior. In that case, she would grab the object to prevent people from getting it. The frequency of the behavior would be increased because it avoids a negative consequence—the loss of access to the object in question. In a different scenario, the behavior might be derived as a result of her predatory inclinations and positive reinforcement of the behavior. That is, her natural tendency to grab something in her mouth and hold it there might be reinforced by peoples' attention. The game goes on as long as she retains the object, and is over the moment she relinquishes it—so she doesn't.
We'll have to leave it to you to determine the precise cause of your dog's behavior, but if she shows signs of willfulness or possessiveness at other times, perhaps the dominance explanation fits better. If you regard her as a dog with a strong prey drive, who likes to be the center of attention, maybe the predatory explanation is more correct. You could also argue dominance with positive reinforcement, or predatory motivation with negative reinforcement.
Originally published in AKC Family Dog in the column "Why Does My Dog Do That?" by Dr. Nicholas Dodman.
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