Wild dogs long ago adopted a hierarchical order that establishes which members get first option on food, the best resting spots and the healthiest mates. So rather than having to fight for access to valued things every time, those lower down in rank know to wait their turn.
That way they not only keep order within the pack, but also keep the pack strong because the best genetics are bred with, while the weaker animals’ offspring may not be as healthy and die earlier.
In our domesticated dogs, the more senior pack members will sometimes show a bit of aggression towards lower-ranking dogs, to remind them of their place. Those right at the top are often so confident of their respected position that they don’t need to display this behaviour, and so many times middle-ranking dogs will be the only ones “reminding” the lower-ranking dogs of their place.
Male dogs are more commonly seen doing this. It’s seen more often in purebreds than in mixed breeds and the most common age 1 – 3 years.
Dogs that do this may sometimes also become aggressive to their human family:
These aggressive displays are likely rooted in a mix of fear and anxiety, and being motivated by frustration and the desire for control.