Survival of the fittest and Darwin's theory of natural selection are clearly the biggest themes in "The Call of the Wild".
We're set in London following Buck, a dog who from the start is in conflict with his surroundings, with humans, as well as with other dogs. His goal in the story is to overcome these challenges and survive. In a way, Buck must learn to be wilder than his environment in order to stay alive. He senses the harshness and brutality of the world around him looking directly at the consequences anyone that fails to adapt could suffer, in the figure of Curly, a good natured and harmless dog who is being crushed by his inability to overcome these conditions.
This tale is a pefect parallel with Darwin's theories, which propose that each species evolves in a way that enables them to overcome the obstacles presented by their environment in order to survive.
Hope this helps!
