Conrad uses Dr Monygham's torture as a platform to make some of Nostromo's most scathingly explicit remarks about the human condition. Here he expresses in full the theme that mankind conquers each other not because of any imperfect social system, but because of primeval, ineradicable human nature ("necessity"); and that idealism ("the growing complexity of their passions") is responsible merely for refining the instinct to a form of sadism, never for removing it from even an instant of history.

Note that in this vision, the primitive man is lazy ("indolent"), and his motive for conquest is presumably to take something produced by his less lazy neighbor. The same process is being enacted and commented upon in the plot with regard to the San Tomé mine.