A Discourse Upon the Origin and the Foundation of the Inequality Among Mankind, by Jean-Jacques Rousseau. Part I.

This work presents Rousseau's belief in the profoundly transformational effects of the development of civilization on human nature, which Rousseau claims other political philosophers had failed to grasp. Specifically, before the onset of civilization, according to Rousseau, natural man lived a contented, solitary life, naturally good and happy. 

It is only with the onset of civilization, Rousseau claims, that humans become social beings, and, concomitant with their civilization, natural man becomes corrupted with the social vices of pride, vanity, greed and servility.