Efficiency is broadly defined as "preventing the wasteful use of a particular resource." The resource may be material (like ivory) or abstract (like physical energy). The concept of efficiency is explicitly referenced just three times in Heart of Darkness: twice in Marlow's preamble to his story of his journey up the Congo, and once with regard to the Congolese laborers.
Marlow begins his story by speculating about how the Roman colonists of ancient Britain must have felt upon entering such a savage and alien landscape, and compares their circumstances to those of modern colonists in the "dark places of the earth." Any colonist in an uncivilized territory is subject to the same fears and corrupting influences, from violence and disease to a kind of moral nihilism brought on by living so far from "civilized" society. The modern colonists differ from their ancient counterparts only in their focus on the goals of their colonization:
"What saves us is efficiency—the devotion to efficiency."
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