Not the strongest; not the cleverest—
Weakness and stupidity everywhere survive.
There is no way of determining fitness except in that a thing does survive.
"Fitness," then, is only another name for "survival."
Darwinism:
That survivors survive.
Although Darwinism, then, seems positively baseless, or absolutely irrational, its massing of supposed data, and its attempted coherence approximate more highly to Organization and Consistency than did the inchoate speculations that preceded it.
Or that Columbus never proved that the earth is round.
Shadow of the earth on the moon?
No one has ever seen it in its entirety. The earth's shadow is much larger than the moon. If the periphery of the shadow is curved—but the convex moon—a straight-edged object will cast a curved shadow upon a surface that is convex.