Man, biologically considered ... is simply the most formidable of all beasts of prey, and, indeed, the only one that preys systematically on its own kind.
William JamesA little cooling down of animal excitability and instinct, a little loss of animal toughness, a little irritable weakness and descent of the pain-threshold, will bring the worm at the core of all our usual springs of delight into full view, and turn us into melancholy metaphysicians.
William James