Survival of the fittest  

The fittest survive.

What is meant by the fittest?

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.

--The Book of the Damned (1919) by Charles Fort

"We, the lineal representatives of the successful enactors of one scene of slaughter after another, must, whatever more pacific virtues we may also possess, still carry about with us, ready to burst at any moment into flame, the smouldering and sinister traits of character by means of which they lived through so many massacres, harming others, but themselves unharmed.... If evolution and the survival of the fittest be true at all, the destruction of prey and of human rivals must have been among the most important of man's primitive functions, the fighting and the chasing instincts must have become ingrained. Certain perceptions must immediately, and without the intervention of inferences and ideas, have prompted emotions and motor discharges; and both the latter must, from the nature of the case, have been very violent, and therefore when unchecked of an intensely pleasurable kind. It is just because bloodthirstiness is such a primitive part of us that it is so hard to eradicate, especially where a fight or a hunt is promised as a part of the fun.... No! those who try to account for this from above downwards, as if it resulted from the consequences of the victory being rapidly inferred, and from the agreeable sensations associated with them in the imagination, have missed the root of the matter. Our ferocity is blind and can only be explained from below. Could we trace it back through our lines of descent, we should see it taking more and more the form of a fatal reflex response, and at the same time becoming more and more the pure and direct emotion that it is."--Principles of Psychology (1890) by William James