Some people have suggested that this famous phrase is a tautology - that is, of the form "an X is an X" and therefore pointless. If it just says "Survivors survive", then the complaints are right. There are three rebuttals:
The Theory of Evolution has never been about survival. What Darwin said was that heritable variations led to differences in reproductive success. Philosophers of science agree that that's not circular or tautological.
For example, Alpheus Hyatt claimed that lineages, like individuals, had cycles of youth, old age, and death (extinction). Decline was programmed in. As maturity leads to old age, the best individuals die, leaving the worst to see the end.
And there was the theory of orthogenesis. It held that certain trends, once started, could not be stopped, even though they led to extinction through increasingly inferior design. For example, Irish elks had enormous antlers. It was held that they had died out because they were unable to stop the size increase. Likewise, the demise of saber-tooths was supposedly because their teeth had gotten longer and longer, until the poor creatures couldn't open their jaws wide enough to use them.
So, "Survival of the fittest" was apparently not obvious until after someone pointed it out.