I just want to add one note.
Darwin originally created the term, NATURAL SELECTION. His contemporary, Alfred Russel Wallace, also independently formulated this. The difference between the two great scientists is that the former did much of his research in South America within the Galapagos Islands. The latter executed much of his research in the Asian Malay Archipelago.
The term SURVIVAL OF THE FITTEST evolved later, and is considered synonymous.
I understand William's commentary that the concept is dangerous. However, neither scientist was trying to promote discriminatory principles. They simply observed that the animals with the greatest reproductive potential, coupled with the greatest self-sustaining characteristics (e.g., hunting mechanisms, defense mechanisms, etc.), were the ones which were the driving force behind evolution.
In the past ten million years, human beings evolved from the common ancestor we share with the chimpanzees, to our current condition of HOMO SAPIENS MODERN. This includes the evolution speech, which we are all exercising herein.