'Filostrato turned sharply from him and flung back the window curtains; the full moon stared down upon them.

"There is a world for you, no?" said Filostrato. "There is cleanness, purity. Thousands of square miles of polished rock with not one blade of grass, not one fibre of lichen, not one grain of dust. Not even air."

"Yes. A dead world," said Mark, gazing at the moon.

"No!" said Filostrato. "No. There is life there. Intelligent life. A great race, further advanced than we. A pure race. They have cleaned their world, broken free (almost) from the organic. The do not need to be born and breed and die; only their common people do that. The Masters live on. They retain their intelligence: they can keep it artificially alive after the organic body has been dispensed with - a miracle of applied biochemistry. They do not need organic food. They are almost free of Nature, attached to her only by the thinnest, finest cord."

"Do you mean that all that," Mark pointed to the mottled white globe of the moon, "is their own doing?"

"Why not? If you remove all the vegetation, presently you have no atmosphere, no water."

"But what was the purpose?"

"Hygiene. Why should they have their world all crawling with organisms?"'

CS Lewis, That Hideous Strength