What we know, in a sense in which we know nothing else, is that the trees and the grass did grow and that a number of other extraordinary things do in fact happen; that queer creatures support themselves in the empty air by beating it with fans of various fantastic shapes; that other queer creatures steer themselves about alive under a load of mighty waters; that other queer creatures walk about on four legs and that the queerest creature of all walks about on two. These are things and not theories; and compared with them evolution and the atom and even the solar system are merely theories. The matter here is one of history and not of philosophy; so that is only be noted that no philosopher denies that a mystery still attaches to the two great transitions: the origin of the universes itself and the origin of the principal of life itself. Most philosophers have the enlightenment to add that a third mystery attaches to the origin of man himself. In other words, a third bridge was built across a third abyss of the unthinkable when there came into the world what we call reason and what we call will. Man is not merely an evolution but rather a revolution. That he has a backbone or other parts upon a similar pattern to birds and fishes is an obvious fact, whatever be the meaning of the fact. But if we attempt to regard him, as it were, as a quadruped standing on his hind legs, we shall find what follows more fantastic and subversive than if he were standing on his head.