That explains why such rules are beneficial, but does not explain how such rules should come about. They date back thousands of years when no one knew the mech

That explains why such rules are beneficial, but does not explain how such rules should come about. They date back thousands of years when no one knew the mechanisms so its not deliberate. It could be evolution of cultures - in that groups that followed certain rules survived better. The first problem I see with that is that the two main religions that ban pork also have a lot of other rules about food, dress and grooming, sexual behaviour, and lots of other things. SOme of them (hygiene rules, for example) are beneficial, but how do you explain the rest. SOme might have less obvious benefits in the context of the society they originated in - but all? The other is that you do not need rules to be religious. Social norms are just as powerful. The persistence of circumcision in the US illustrates this. It is still common (usual?) despite the largest religion not only not requiring, but its scriptures specifically state it is not a religious requirement (and dispenses with the entire set of detailed rules - retaining only some more general ones).