First I want to show that Darwin used this phrase:
“Darwin used the term “natural selection” in his book “On the Origin of Species” but was persuaded that Spencer's phrase ”survival of the fittest”
was probably 'more convenient' “http://www.perceptions.couk.com/genes1.html#rst
“Darwin did not believe that the environment was producing the variation within the finch populations. He correctly thought that the variation already existed and that nature just selected for the most suitable beak shape and against less useful ones. Darwin and his supporters ultimately described this process as the ”survival of the fittest.”
This is very different from Lamarck's incorrect idea that the environment altered the shape of individuals and that these acquired changes were then inherited.”http://anthro.palomar.edu/evolve/evolve_2.htm
Look at this chapter from Darwin's own book
On the Origin Of Species (1859)
Chapter IV: Natural Selection; Or the Survival of the Fittest http://www.infidels.org/library/historical/charles_darwin/origin_of_species/Chapter4.html
From the same source
This preservation of favourable individual differences and variations, and the destruction of those which are injurious, I have called Natural Selection, or the Survival of the Fittest.
What is wrong with this? It's a tautology.
“From time to time, attacks on neo-Darwinism are mounted, usually by persons who either see evolutionary theory as antireligious or who basically misunderstand Darwin's theory. One attack, entitled “Darwin's Mistakes,” by Tom Bethell, was published in Harper's magazine.
Bethell began by pointing out that Darwinian theory is a tautology rather than a predicative theory. (The term tautology means a statement that is true by definition.)* That is, evolution is the survival of the fittest. But who are the fittest? Obviously, the individuals who survive. Thus, without an independent criterion for fitness, other than survival, we are left with the statement that evolution is the survival of the survivors. This indeed is a tautology. But it is possible to assign independent criteria for fitness. Darwin wrote extensively about artificial selection in pigeons, in which the breeders' choice was the criterion for fitness. (Many novel breeds of pigeon have been created this way.) Artificial selection has been practiced extensively by plant and animal breeders. Here too, survival is not the criterion for fitness, productivity is.”
Robert H Tamarin, (1996) “Principles of Genetics” (5th ed), p571.
Interestingly here the item that recognises the term as a tautology uses a bad analogy to show 'natural selection'; 'artificial selection'. Evolutionary arguments fail in this realm.