Chapter II - Man's Sole Impulse--the Securing of His Own Approval [Mark Twain's essay: What Is Man?]
(Mark Twain essay, "What is Man" where he argues that all acts are always necessarily selfish, and that no one is capable of acting except to secure their own approval. Good stuff)
"Ah, those endless forests, and their horror-haunted gloom! For what eternities have I wandered through them, a timid, hunted creature, starting at the least sound, frightened of my own shadow, keyed-up, ever alert and vigilant, ready on the instant to dash away in mad flight for my life. For I was the prey of all manner of fierce life that dwelt in the forest, and it was in ecstasies of fear that I fled before the hunting monsters."
Jack london, "Before Adam"