As most of my readers know, I sometimes like to watch nature shows. Over the years I have noticed that there is one practice that is not found in the minds or behaviors of any living organism except man, the practice of self-sacrifice. If you look at single-celled creatures you will never see say an amoeba sacrifice itself for the sake of a paramecium or even another amoeba. It just doesn't happen. Over in the plant world it's the same way. You'll never see a Rose bush sacrificing itself for a Petunia or giving up its thorns so some needy animal can eat it. Nor will you see an Oak tree sacrificing itself for an Elm or any other being.
More of the same can be seen in the animal world. A worm does not sacrifice itself to a bird or to anything else. Cats don't sacrifice themselves to dogs or vice-versa. And so it goes throughout the realms of all livings things. There is a complete absence of self-sacrificial behavior. It's rather obvious that nature did not evolve such a behavior in any of its organisms precisely because that behavior is antithetical to the organism's survival. It is so for man as well.
If you look closely at the behaviors of all of these organisms you will readily see that every action they take is a self-interested action, that is, an action determined by their natures to sustain and/or enhance the organisms' lives. It follows then, that man, being an organism too, must have a specific nature which can guide his actions in a similiar self-interested way. It was Aristotle who correctly identified man as the rational animal but it was Ayn Rand who clarified what that implied and identified a self-interested behavior (moral code) proper to a rational animal, rational self-interest, i.e. a non-sacrificial way of life.
But man is unlike the animals in that he must choose his behavior. If man can choose to adopt such a non-sacrificial code, he too will become at peace with his nature. No living organism choses to act against its nature. Only man has that ability and he has spent most of his history doing so with self-sacrifice. There is a non-sacrificial way of life proper to man's nature, rational self-interest, and man needs to explore it now.