1
general::
Those best adapted to particular conditions will succeed in the long run, as in They've had to close a dozen of their stores, but the ones in the western part of the state are doing well? it's the survival of the fittest. This phrase was invented by Herbert Spencer in Principles of Biology (1864) to describe Charles Darwin's theory of natural selection of living species. By the early 1900s it was being transferred to other areas.
American Heritage Idioms
2
general::
Phrase(s): the survival of the fittest
the idea that the most able or fit will survive (while the less able and less fit will perish). (This is used literally as a principle of the theory of evolution.) • In college, it’s the survival of the fittest. You have to keep working in order to survive and graduate. • I don’t give my houseplants very good care, but the ones I have are really flourishing. It’s the survival of the fittest, I guess.
McGrawhill's American Idioms And Phrasal Verbs