One way in which this play could be related to the Darwinian concept of survival of the fittest is through the play's examination of class and how it looks at two characters who seem to be rather unhappy about where they are placed in the social ladder. The Darwinian concept of the survival of the fittest states that there will be some members of a species who, thanks to their genetic variations, will be more suited to prosper and survive better than others. Applying this to humans led to the theory of Social Darwinism, which allowed people to argue that those who prospered were just better adapted to suit their environment.
The main character to focus on in this play would be Jean, who is greatly dissatisfied with his position as a servant. He has a dream of trying to climb a tree in order to obtain the golden eggs that lie at the top. He desires to become a member of the aristocracy and does everything he can to obtain this goal, speaking with a sophisticated accent and trying to form plans to gain money and social status.
However, both Jean and Julie are forced to realise that they are unable to move social spheres. They are left to dwell in the rung on the social ladder that their birth dictated. Strindberg clearly shows that there is no changing the class you are born into and how that impacts your life. Darwinianism could therefore be related to class, which is a key theme in this play.