C.S.
I think the fittest survive and the others die.
I think you are oversimplifying the term "fittest survive"
There are thousands of individual traits under pressure by hundreds of thousands of enviromental factors that can plausibly ruin a creatures chancee to reproduce and thus continue the species. It is a simple fact of nature that there are more ways for a thing to go wrong than right as pertains to reproductive success.
The fittest is the one who's capabilities best deal with the constantly changing facets of nature.
™ Version 4.2