That’s the C.S. Lewis argument in a nutshell (good summary btw). I simply think it’s learned behavior. Even dogs travel in packs, various lower creatures cooperate with each other in hunting, rearing their young, etc. Do these creatures have souls? If they do the bible certainly doesn’t tell us this.
Just another paraphrasing of scholastic theology.
Lower forms of life cooperate with each other purely out of survival instinct as a species and not out of any moral sense or knowledge of what is right and wrong. In the animal kingdom creatures do not feel that they
ought to cooperate with each other for the good of the pack or herd or out of consideration for each other. A dominant male lion, for instance, will confront and chase off another male lion so that it can mate with the lioness the weaker lion was with. And before it mates with her, it kills the cubs that were produced by the former lion. The lioness simply responds without any qualms about the destruction of her cubs. The new pair mate as if nothing wrong had happened. Normal human beings would never do such a thing because of their sense of right and wrong and their moral compulsion. Is such behavior in itself based on a sense of what is good for the herd? No, it’s based purely on animal instinct without any thought given to what is just or fair: the instinct to mate and sire one’s own cubs. If that dominant male lion had any *charitable * feelings towards the other lion, the lioness, and her cubs, it wouldn’t have behaved as it did. Charity is a human virtue possessed and exercised by beings who have souls. And so a normal or enlightened human being cannot act so uncharitably without feeling the pangs of conscience and emotional discomfort.
Our morality is formed by ourselves; and nothing else. Like dogs we learned that** it’s more efficient and conducive to our survival if we cooperate**. We had larger brains and vocal cords capable of speech, so through our cooperation and biological intelligence we slowly progressed (and not only in technological terms; but also in areas like socialization and rules aimed toward a pragmatic coexistence).
Morality is like mathematics which has an objective existence apart from the subject who eventually learns to add and subtract. And because math is something learned or acquired as a body of knowledge, it doesn’t make it a human convention no more than morality. Morality is no more subjective than mathematics is. The only difference between the two is that the former is concerned with what should be, not with what is factual. (cf. Mr. Lewis)
Morality is a notion that is spontaneously acquired at some point and expressed in some relative form. Human beings may not always agree with each other on what they think is right or wrong, but nonetheless these pure notions exist as objective standards above and apart from individual differing viewpoints. We may not always cooperate with each other because our beliefs in what is good for the whole may differ according to our individual conscience. However, it’s better to listen to a well-informed and healthy conscience. A corrupt conscience can be the cause of a faulty equation: 2+2=5. This can be translated into free abortion on demand. And unlike a cur, one can refuse to exercise his obligation to vote because of his lack of faith in the political parties of his country which he feels don’t really care for an unprotected minority, the unborn, by not making the effort to reinterpret the Constitution. Can you imagine the political state of any country if everybody refused to vote like him? But people do vote out of a sense of responsibilty, unlike the mutt, and not simply out of pragmatic reasons - not that dogs have them in spite of what we may perceive to be their practical aims. Many people feel that it would be
selfish of them not to vote given the thought that they have a social obligation to exercise their right to vote, regardless of their lack of faith in their leaders, to preserve the political stability and welfare of their state.
The whole idea of socialization and rules for the good of society brings us back to the question of right and wrong. A sense of moral responsibilty must come first if there are to be any rules of conduct governing social behavior. You are suggesting that we are simply cooperating with each other so that each of us can benefit personally in the ordered group. But if we are only cooperating out of personal interest, protecting ourselves from each other, with no regard for the other individuals who belong to our group, we could be accused of being selfish. And if we were asked why we shouldn’t be selfish by being indifferent to the other members of our group, we would honestly have to answer
Because it’s wrong. A dog in a pack is only acting out of instinct for its own survival or the preservation of its species with absolutely no personal regard for any of the other individual dogs it has banded with. A b-tch will devour its puppies out of instinct if the preservation of its species is either threatened or rendered futile by her litter. It isn’t a question of morality with lower forms of life, so how can you draw an analogy between them and us?

If I were to put a bullet in my own head to avoid being captured by the enemy and divulging the whereabouts of my comrades under torture, I know that my act would be immoral in spite of my good intentions. With animals there is no such thing as good intentions and the question of what is right and wrong in view of them.