'MORAL LAW'
C.S.Lewis wrote much about a Law of Human Nature, or 'Moral Law'.
This is something within us that compels us to goodness.
It is unlike instinct, which is inherited from our parents and may impel us in different directions. Instinct takes hold when we witness an assault, for instance. One desire, derived from our herd instinct, is to help the victim. Another desire, derived from our instinct for self-preservation, is to protect ourselves and to stay clear. But, separately from our instinct, the Moral Law coerces us to do the right thing. This is something we feel inside us. It tells us to follow the impulse to help, and suppress the impulse not to assist. The Moral Law can explain why prisoners of war were kept alive and other inexplicable acts of compassion.
It is why humans have a curious idea that they ought to behave in a certain way, and cannot really get rid of it. You may want to stay safe rather than save a man who is drowning, but the Moral Law tells you to help him all the same.
The Moral Law is something innate. It is not something we learn, it is something we cannot discard. Even if we do not obey the Moral Law - if we do not do the right thing - it will remain as a voice inside our heads, conveying a feeling of guilt.
Some of this behaviour could be attributed to altruism - the selfless concern for the welfare of others or, in evolutionary study, the behaviour of an individual that, while decreasing the fitness of that individual, increases the fitness of another. I gave a definition that refers to evolution because altruism does indeed have an evolutionary explanation. For instance, in a group of Australian Aboriginals, or Siberian Inuits, altruism towards other group members was found to improve the overall fitness of the group. Since the group becomes fitter with altruistic behaviour, altruism can be explained as a characteristic that has evolved.
But the Moral Law also includes instances of behaviour that provide no conceivable positive value to either an individual or a species. Humans appear to possess something additional to the altruism found in other species. This add-on quality lies at the heart of the Moral Law.
The moral teachings of the ancient Egyptians, Babylonians, Hindus, Chinese, Greeks and Romans are very similar to one another and to our own. That's because the Moral Law exists in all humans all over the planet. But, again, although all humans are forced to believe in a real right and wrong, and that they should behave in a certain way, they do not in fact behave in this way. They know the Moral Law, and they break it.
The Moral Law and the fact that we break it are the foundation of all clear thinking about our universe and ourselves (Andrew Parker, Genesis Enigma).