Ultimately our moral sense or conscience becomes a highly complex sentiment – originating in the social instincts, largely guided by the approbation of our fellow-men, ruled by reason, self-interest, and in later times by deep religious feelings, and confirmed by instruction and habit.

Source:Part I. The Descent or Origin of Man, Chapter V. On the Development of the Intellectual and Moral Faculties during Primeval and Civilised Times
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