We know that traits like intelligence, and beauty, and courage, are, at least partially, genetic.
And obviously, the best amongst us should lead. The head should lead the tail.
So, a prince could be genetically programmed from birth to be a great king, and raised from birth to fulfill that responsibility better than anyone else.
This frees up the rest of us to genetically program our children and raise them from birth to pursue other endeavours, like art, or science, or agriculture and husbandry.