Civilization vs. Savagery
A major theme of Heart of Darkness is civilization versus savagery. The book implies that civilizations are created by the setting of laws and codes that encourage men to achieve higher standards. It acts as a buffer to prevent men from reverting back to their darker tendencies
Civilization, however, must be learned. London itself, in the book a symbol of enlightenment, was once "one of the darker places of the earth" before the Romans forced civilization upon them.
While society seems to restrain these savage tendencies, it does not get rid of them. These primeval tendencies will always be like a black cloth lurking in the background.
The tendency to revert to savagery is seen in Kurtz. When Marlow meets Kurtz, he finds a man that has totally thrown off the restraints of civilization and has de-evolved into a primitive state.
Marlow and Kurtz are two opposite examples of the human condition. Kurtz represents what every man will become if left to his own intrinsic desires without a protective, civilized environment. Marlow represtens the civilized soul that has not been drawn back into savagery by a dark, alienated jungle.
The book implies that every man has a heart of darkness that is usually drowned out by the light of civilization. However, when removed from civilized society, the raw evil of untamed lifestyles within his soul will be unleashed.
The underlying theme of Heart of Darkness is that civilization is superficial. The level of civilization is related to the physical and moral environment they are presently in. It is a much less stable or permanent state than society may think.