turtles all the way down

The novice asks the master, "Oh wise one, what keeps the world from falling into the abyss?"

The master replies, "The world is supported on the back of a giant turtle."

"But what supports the giant turtle, master?"
"Another turtle, my child."
"And beneath him?"
"Sorry, it's turtles, all the way down."

Begging the question is a phrase I heard more often than I understood. That's what this is.

Intelligent design similarly relies on an infinite stack of turtles. If a structure is (seemingly) too complex to have evolved by natural selection, it must therefore have been designed by an entity that is in turn too complex to have evolved by natural selection. And who designed this entity?

Sorry, it's intelligent designers, all the way down.

(With thanks to Crawford Washington.)