The correct answer is: "Darwinism".
The concept of the survival of the fittest is central in the theory of the evolution of the species developed by Darwin. But it has also been applied many times in the economic sphere, for the defense of competiton and to promote the establishment of free markets.
The evolutionary theory states that those spices that develop favourable traits would be able to survive, while weak ones would extinguish. The same understanding is applied in economics, where those who are able to gain profit in the markets, given a certain endownments of inputs would suceed while those who are not able to obtain any profit would sink.