The dual nature of man, acting appallingly but being appalled at it, is what proves we are not the products of evolution alone. Nature does not teach the latter. Meteors are not appalled at their destruction. Wolves are not appalled at their carnage. It is their nature. We have nature and supernature. The supernature does not emerge from nature as a development but is injected from above to produce the conflict. Evolution, the selfish gene, account for selfishness but not selflessness, as selflessness is not merely a more sophisticated form of selfishness, enlightened self-interest, but an absolute contradiction to it. Selflessness will not just compromise here and there to get its own way ultimately but will willingly sacrifice itself gaining nothing in return simply because it is the right thing to do.
It is this recognition of one's true higher nature that enables one to look unsparingly at the lower nature. If all there is is our natural self, the horror would be too much to bear.