“Katz had read extensively in popular sociobiology, and his understanding of the depressive personality type and its seemingly perverse persistence in the human gene pool was that depression was successful adaptation to ceaseless pain and hardship. Pessimism, feelings of worthlessness and lack of entitlement, inability to derive satisfaction from pleasure, a tormenting awareness of the world's general crappiness: for Katz Jewish paternal forebears, who'd been driven from shtetl to shtetl by implacable anti-Semites, as for the old Angles and Saxons on his mother's side, who'd labored to grow rye and barley in the poor soils and short summers of northern Europe, feeling bad all the time and expecting the worse had been natural ways of equilibriating themselves with the lousiness of their circumstances. Few things gratified depressives, after all, more than really bad news. This obviously wasn't an optimal way to live, but it had its evolutionary advantages.”

“depression was a successful adaptation to ceaseless pain and hardship [...] feeling bad all the time and expecting the worst had been natural ways of equilibrating themselves with the lousiness of their circumstances. Few things gratified depressives, after all, more than really bad news [...] Grim situations were Katz's niche the way murky water was a carp's [...] he might well have started making music again, had it not been for the accident of success. He flopped around on the ground, heavily carplike, his psychic gills straining futilely to extract dark sustenance from an atmosphere of approval and plenitude.”

“Nesse’s research focuses on the evolutionary origins of depression. Why does depression exist at all? If it’s stayed in our gene pool for so long, he argues, there must be some evolutionary benefit. Nesse believes that depression may be an adaptive mechanism meant to prevent us from falling victim to blind optimism—and squandering resources on the wrong goals.11 It’s to our evolutionary advantage not to waste time and energy on goals we can’t realistically achieve. And so when we have no clear way to make productive progress, our neurological systems default to a state of low energy...”

“If Rome, a city of the vulgar living, had been depressing after Greece, London, a city of the drab dead, was fifty times worse. ”

“This story ["The Depressed Person"] was the most painful thing I ever wrote. It's about narcissism, which is a part of depression. The character has traits of myself. I really lost friends while writing on that story, I became ugly and unhappy and just yelled at people. The cruel thing with depression is that it's such a self-centered illness - Dostoevsky shows that pretty good in his "Notes from Underground". The depression is painful, you're sapped/consumed by yourself; the worse the depression, the more you just think about yourself and the stranger and repellent you appear to others.”

“...that manic depression, far from being a liability was an advantage. It was a selected trait. If it wasn't selected for, then the "disorder" would have disappeared long ago, bred out of the population like anything else that didn't increase the odds of survival. The advantage was obvious. The advantage was the energy, the creativity, the feeling of genius, almost, that Leonard felt right now. There was no telling how many great historical figures had been manic-depressives, how many scientific and artistic breakthroughs had occurred to people during manic episodes.”