Very seldom, only in rare moments of clarity, only after ages of misapprehension, did a few of them, here and there, now and again, begin to have the deeper insight into the world's nature and man's. And no sooner had this precious insight begun to propagate itself, than it would be blotted out by some small or great disaster, by epidemic disease, by the spontaneous disruption of society, by an access of racial imbecility, by a prolonged bombardment of meteorites, or by the mere cowardice and vertigo that dared not look down the precipice of fact.

Chapter XIII: Humanity on Venus; Section 1, Taking Root Again (p. 195) - Last and First Men (1930)