Like a pack of wolves, a pride of lions, or a troop of monkeys, we humans learn to fight, wrestle, push, shove, and negotiate first with our siblings. If not brothers and sisters, then with cousins or other members of the family group that are close to our age. We, little kids, are always vying for the most attention from mommy and daddy and are willing to put on quite a show to get it. We learn valuable social skills during these early development years. The best wrestlers or the oldest sibling may at first, end up being the leader for a while by just using brute force. This may not last long, as kids grow to larger and larger sizes, as they get older. Sex makes no difference as to who is the leader in the sandbox either. The difference, eventually, is who is the best negotiator. What we learn before the sandbox and interaction with kids, who are not relatives, is the lessons of "sibling rivalry".
A brother and sister fighting over the same toy is not about that toy. It is over whom mom says she will give the toy to, so that the fight stops. It is about who wins the attention from mom. We humans are very competitive by instinct. We want to win at everything. "Who ever dies with the most toys wins" is a famous quote. Oil, cattle, money, spouses, slaves, land, natural resources, power, water, and any other item deemed of value to someone else are worth negotiating, fighting, or eventually killing for. All these things of valve started off as my brother's toy, that I wanted and schemed to get my mother to take it away from my sibling and bestow on me, her favorite. In that historical fiction novel called the Old Testament, Cain killed Abel his brother over "sibling rivalry".
So, what do all these references to genetics mean? Simply, Mommy and Daddy and their decisions, in the living room, in front of the TV, after a full day of stressful decision making, on which little crying brat gets that damn toy, may be helping to shape the decisions of the future leader of the free world. Remember to keep it simple (KISS). It is the same rotten deal for all. Let them find their own way. Land the helicopter mommy and let them fight it out. It is only normal.