Of course, Darwin's Theory of Evolution has many points that correspond with Naturalism, including the survival of the fittest. Let us just remind ourselves of what Naturalism is. Naturalism is a movement that originated in the nineteenth century and focussed on the ideas of thinkers such as Darwin. They concluded that human behaviour is determined by heredity and environment. Key themes of Naturalism involve presenting human beings as mere players in a world where they are controlled by natural forces of which they have little understanding or comprehension. Key writers who can be described as Naturalist are Jack London and Stephen Crane.
Of course, we can see the relation to the survival of the fittest, as Darwin argued that creatures survive on the basis of their genes alone, rather than their intelligence or wit.