Perhaps one of the most terrifying aspects of Heart of Darkness is the dehumanization of its characters. Conrad shows this by sucking the humanity out of his villains – the manager, the accountant, the brickmaker, and Kurtz. At some point in the text, each character lacks some fundamental human characteristic – whether it is compassion, understanding, or (Marlow’s favorite) restraint. This suggests that at some level, these characters have been so degenerated by their own greed and their time in the interior that they have become less than human. They are shells of their former selves, hollow within.
Men go into the interior whole and unscathed, but while living there, the hostile wilderness drains them of their humanity.