"Struggle for existence" and "Survival of fittest" are associated with

The correct option is D Darwinism

The struggle for existence: As a consequence of this prodigal rate of reproduction, Darwin reasoned that there must be a competition between individuals belonging to the same or other species, for sharing food, water and living space. Every individual puts efforts for fulfilling the basic needs such as space for living, food for a living, mate for reproduction and also protection from enemies. This competition is known as 'struggle for existence'.

Survival of the fittest: Only those organisms, which have favourable variations, are at a specific advantage over others. Such individuals survive the struggle for existence while those, which are less adapted or not adapted, get eliminated. This idea came to be known as 'survival of the fittest'.