Catholic popes who lived debacherous lives propagated successfully, while those lower in the church heirarchy actually adhered to abstemious behavioral guidlines to which the pope paid lip service. Those poor saps' genes failed to propagate themselves. I think it's a mistake to confuse memes and genes.
Genetic evolution acts on a times scale much larger than cultural evolution.
Talking about reproductive fitness gets a little complicated in a cultural setting. Memetics is an interesting idea becuase it changes our conception of what it is that makes each of us unique. In the past it was held that immortality, after a fashion, was obtainable through children. Memetics argues for a different emphasis. Immortality is to be obtained in the procreation of ones ideas.