Pitchounette - very interesting your observation about 'pack of wolves'. I do strongly agree that young humans behave in that way and establish pack pecking orders within a family
I wrote the other day on a thread about a family we know where the DS1 age 9 is extremely (and sneakily) violent to DS2. The DS1 insists on sitting where he wants at dinner and even displaces his father. The DS2 is very frightened and appeals to his mother for protection while DS1 is very disrespectful to her if she steps in to protect DS2.
It ties in what Piscesmoon said and agree again about rough and tumble play among young bears. However, I still strongly feel that 'play' fighting among boys is not actually play at all it is about physical domination of another and is not actualy 'needed' by boys.
I have also seen it among boys who play football unsupervised in the playgrond. It is a proxy for violence where actual fighting is formally forbidden. Kicking someone or pushing them to the floor whle 'playing' football is too often a form of undercover fighting that is tolerated by schools. I know one very good boys school that carefully supervises and limits the amount of playground football boys are allowed to play for this very reason.
I should ALSO say that girls do 'play fighting' in a different way that sorts out pecking orders and can be equally cruel.