Bryan Caplan says "the most prominent conclusion of twin research is that practically everything—health, intelligence, happiness, success, personality, values, interests—is partly genetic." He uses that research to argue that parents should have more children and spend less time on each of them:
I call it “Serenity Parenting”: Parents need the serenity to accept the things they cannot change, the courage to change the things they can, and (thank you twin research) the wisdom to know the difference. Focus on enjoying your journey with your child, instead of trying to control his destination. Accept that your child’s future depends mostly on him, not your sacrifices. Realize that the point of discipline is to make your kid treat the people around him decently—not to mold him into a better adult.
Will Wilkinson masterfully deconstructs the heart of Caplan's argument.