"survival of the fittest" term coined by Herbert Spencer, referring Darwin's theory of "Natural Selection" became an expression which led path to wider research area in fields of biology (genetics), understanding evolution forming its niche.
Although Darwin's "Natural Selection" only mentioned of biological aspect,
Evolution by natural selection is a process demonstrated by the observation that more offspring are produced than can possibly survive, along with three facts about populations:
1) traits variation among individuals
2) different traits leading different rates of survival and reproduction, and
3) traits can be passed to successive generations.
thinkers, sociologists (social scientists) interpreted the theory in different aspects; among of which, some explanation, were apart form Darwin's explanation to which he opposed in his lifetime. As after his death, there is no bar on proposing explanations supporting ideas and even their Propaganda as of Anarchism, Racial Superiority (Racism), eugenics
The time some ideas struck to write about Darwinism, little was known about it to me, and after studying about it and its concerning topics I would say much has already been said about it.
What I see it today as :
Consider of sportsperson, athletes, they practice hard in sessions, competing other individuals facing same circumstances. one who strives consistently, struggles, goes beyond limit of self, adapts the unfavoring conditions. then gets selected being favored by nature due to his adaptability (i.e. Natural Selection); finally wins in competition leaving others behind.
here success owes to physical fitness (physical adaptability)
For survival in long run one also need psychological fitness, ability to make decisions, facing difficult situation. physio-psychological condition as a whole works in fitness
Darwinism Influencing Despotic Governments
"survival of the fittest". the expression speaks of, as I see, defense of a particular group from unfavorable situations , and soon they get self sufficient they form a urge of attacking approach for the neighboring communities, to exploit nature. they see it as "attacking is best defense" whether or not others bother for same. they put it as- being fit of being civilized early, it is duty on their shoulders to rule the unfit (uncivilized) persons, as if it were a moral obligation on them.this leads to imperialistic ideas.
Darwinism supporting Racism
we also see here somewhere there comes an ideas of racial superiority. Hitler led Nazi Germany and shown much cruelty to Jews as he see it as inferior race to Aryans. he led an Authoritarian government. Romani people also have to face much of racial-discrimination from centuries.
with time anarchist aspect is also being seen; but I see Darwinism has much influenced Anti-philanthropic nature of government,be it be any monarchic, authoritarian, totalitarian oligarchy or even military rule. Anarchism explanation doesn't well suited in Darwinism
Contributing to Racism and Imperialistic ideas Rudyard Kipling had mentioned in his poem "The White Man's Burden" that - being racially superior and civilized people of Europe, it become their (White Man's) duty (moral obligation) to civilize the "Third World"
Take up the White Man's burden, Send forth the best ye breed(1st para of the poem)
Go bind your sons to exile, to serve your captives' need;
To wait in heavy harness, On fluttered folk and wild—
Your new-caught, sullen peoples, Half-devil and half-child
P.S. : It's a individual view. Please refer to appropriate sources for much of Knowledge gaining purpose