The theory of survival of the fittest?

Answer 1

That is just another name for Charles Darwin's theory of natural selection--i.e., evolution. The term is often misunderstood by the public and misconstrued by people with ideological-based biases wishing to reflect evolution in a negative light. Here, "survival of the fittest" doesn't refer to the biggest and strongest, but to the individuals who survive longer and pass on more offspring. For example, elephants are by far the most powerful land animals in the world, but there is no way that they could survive under water, where it is populated by fish. Though much, much weaker than elephants, fish are better suited to the underwater environment because they have special adaptations like gills, fins, and air bladders. This means they are more fit than the elephant in this context because they will thrive in this environment and will produce more offspring.