Then again, harassing someone who depends on you is entirely different.
Then again, bullying someone so that you ensure pecking order and he does what you want and is beneficial for you a bit more in situation with scarcity is different too.
Suburban middle schools kids did not invented cruelty nor mockery nor ostracization nor beating other kids up. My grand parents remembered such stories. Old books contains such stories. If anything, this get worst with bad situations - hunger or war. There is no reason to think primitive people were somehow magically honorable and noble.
Look at how much constant violence and bullying there is between any siblings when an adult isn't around to stop it.
Back then, kids would need to rely on each other more, no?
Nowadays, what good is a sibling really?
Read no further than the histories of nobles and their feuds and murders to see how bad the best families were.
Given that even in good years a large portion of the population was malnourished in whatever time period you want to pick before the middle of the 20th century, the rich were always better off than the poor and rich families were better than poor ones.
The implication made uphtread is that the rich were best in terms of (lower) intrafamilial conflict. One might assume that wealth produced that effect, one might also assume that the rich were more dependent on social status and property for support, while the poor were more dependent on having close relations who could give aid and lacked assets to fight over, thus leading to less intrafamilial conflict than among the rich.
Applying the fad buzzword for children being mean to each other in suburban middle schools to primitive human culture isn't exactly a valid comparison.