" The green man said, “I’m a fool, I suppose, to put any confidence in you. And yet I do. I am a free man, come from your own future to explore your age.” “That is impossible.” “The green color that puzzles your people so much is only what you call pond scum. We have altered it until it can live in our blood, and by its intervention have at last made our peace in humankind’s long struggle with the sun. In us, the tiny plants live and die, and our bodies feed from them and their dead and require no other nourishment. All the famines, and all the labor of growing food, are ended.” “But you must have sun.” “Yes,” the green man said. “And I have not enough here. "

― Gene Wolfe , Shadow & Claw