Nice one brother. When people say stuff like "it's human nature to pursue self-interest", even assuming that's true, it's very broad. Individuals have different standards for what satisfies them, so their self-interest can lead them in very different directions.
I have read that when a pregnant mother's cortisol levels are high, the baby will react by developing an angry, competitive "nature" or predisposition. The cortisol signals to the child that you've got to be tough in this world. So when a child is born and raised in a loving environment, that's when magic happens.
Absolutely! Whatever the environment tells them is what is necessary/beneficial will be where their self-interest directs them to, so the rules of the game determine the behavior, even assuming a 100% tendency towards self-interest.
That would certainly make sense that those early stressors would play out in that way later in life. The concept of the 7 generation ripple, from so many different indigenous cultures, seems like something that has basically been scientifically proven at this point.