<P> In The Man Versus The State, Spencer used the phrase in a postscript to justify a plausible explanation of how his theories would not be adopted by "societies of militant type". He uses the term in the context of societies at war, and the form of his reference suggests that he is applying a general principle . </P> <P> "Thus by survival of the fittest, the militant type of society becomes characterized by profound confidence in the governing power, joined with a loyalty causing submission to it in all matters whatever". </P> <P> Though Spencer's conception of organic evolution is commonly interpreted as a form of Lamarckism, Herbert Spencer is sometimes credited with inaugurating Social Darwinism . The phrase "survival of the fittest" has become widely used in popular literature as a catchphrase for any topic related or analogous to evolution and natural selection . It has thus been applied to principles of unrestrained competition, and it has been used extensively by both proponents and opponents of Social Darwinism . </P> <P> Evolutionary biologists criticise the manner in which the term is used by non-scientists and the connotations that have grown around the term in popular culture . The phrase also does not help in conveying the complex nature of natural selection, so modern biologists prefer and almost exclusively use the term natural selection . The biological concept of fitness refers to reproductive success, as opposed to survival, and is not explicit in the specific ways in which organisms can be more "fit" (increase reproductive success) as having phenotypic characteristics that enhance survival and reproduction (which was the meaning that Spencer had in mind). </P>

Survival of the fittest is a theory proposed by