You still do not understand the term "fittest". This part of Darwin's theory has nothing to do with physical ability, size, or even one member of a species being overpowering of others in that species. It is simply the "fittest" genetic adaption for the environment. For instance, small mouse-like creatures were at the bottom of the food chain, but when the environment changed, they had genes that made them more "fit" to survive and their predator enemies died out. That is survival of the fittest.
This tired "social darwinism" stuff has been debunked hundreds of times. Darwin's scientific theory had nothing to do with civilization or society, merely explained why there are different "races" of homo sapiens just as there are different "races" of wolves and different "races" of Walruses - nearly identical DNA with very slight skeletal and skin/fur differences.
"In the beginning of a change the patriot is a scarce man, and brave, and hated and scorned. When his cause succeeds, the timid join him, for then it costs nothing to be a patriot."--Mark Twain