Now actually the phrase “survival of the fittest” doesn’t come from Darwin himself, but it comes from Herbert Spencer, who was one of the great popularizers of Darwinism in the late nineteenth century and he introduced that idea. And it’s actually not a very good description of what happens in biology. But people have picked up on that idea. And of course it was picked up by the Kaiser during the First World War, and the idea that “might is right.” And so that was one of the ideologies that were used to justify German militaristic expansion during the first world war.
What is a better description for what happens in biology? You know that biology does use that phrase? If there is a better description, what is it?
You are right to say that survival of the fittest did not originate with Darwin, BUT he did incorporate it into the Origin in the second edition as a synonym for Natural Selection, so he did accept and approve this term, although I read that he had some second thoughts. He called Natural Selection a struggle or “the war of nature” at the end of the Origin.
If Darwin gave race scientific status, that was a mistake that he is responsible for, but others misused this for their own purposes. Other issues are “Social Darwinism” and Eugenics. Hitler got his cues from eugenics and it was popular in many countries. It still has a following.
Survival of the Fittest was encouraged by the British imperial ethos of the time of Darwin and the competitive ethos of Adam Smith. I still wonder why evolutionary science has not seen fit to make an explicit correction of Darwin, Spencer, and Dawkins on this aspect of the science.