natural selection vs survival of the fittest

natural selection and survival of the fittest both are nouns.

Word	Noun	Adjective	Verb	Adverb
natural selection	Yes	No	No	No
survival of the fittest	Yes	No	No	No

As nouns, natural selection and survival of the fittest are synonyms defined as:

natural selection and survival of the fittest: a natural process resulting in the evolution of organisms best adapted to the environment

Other synonyms of natural selection include selection, survival.

natural selection (noun)	survival of the fittest (noun)
a natural process resulting in the evolution of organisms best adapted to the environment	a natural process resulting in the evolution of organisms best adapted to the environment