The way to do this is to formulate the theory in terms of acceptance by new generations of humans. So we compare the respective “teaching costs” of alternative codes, on the assumption that these codes will be taught to children who have not already been educated to accept a moral code. We are to imagine the children start off with natural (non-moral) inclinations to be very partial towards themselves and a few others. We should also assume that there is a cognitive cost associated with the learning of each rule.