How is the selfish gene a hypothetical construct? It's no more theoretical than the statement that every single one of Tony Fabris' ancestors lived long enough to reproduce, every single last one of them all the way back to the beginning of time. Every single one of them managed to survive against all odds, one after the other.

The concept of the selfish gene is that it deploys whatever mechanisms/techniques necessary to ensure the survival of itself, creating such things as society and culture.
The expressed characteristics that allow for its survival and reproduction (morality, ethics, culture, society, as well as lower order characteristics like male/female differences, physical characteristics..) well out of the code. Religionists would rather believe that if genes do exist, they are no more than physical blueprints, and that the hand of God, or at least some higher being(s) have some play in the guidance of all of the above, and genetics is no more than physical blueprints if you will. (To some extent the nature vs. nurture argument is related).

So the question is not whether morality is natural or unnatural... Is morality the result of a complex mixture of genetics and society and culture, where society and culture also result from genetics ultimately? Or is morality not part of the selfish gene at all? If so, then morality and ethics may not be about selfishness of survival (survival of the individual, the family, culture and society) but rather originates from some higher unselfish place (let's call that religion). You might say then religion influences, or perhaps engenders society and culture and carries the blueprint (genetics) as part of this plan. In either case, it can be argued as natural.

Calvin