The Hairy Ape explores themes of class discrimination and naturalism. Yank and the other "blokes" in the "stokehole" rail against the powerbrokers of the world, cursing and threatening to 'bust 'em all," apparently in an attempt to equalize the social ranks. O'Neil's description of the firemen suggests their strong relationship with great apes. Their kinship associations with monkeys reflects an animalistic theme of naturalism that contends that, as members of the animal kingdom, all people can, in certain dehumanizing circumstances, be reduced to primordial animal levels where they must rely on instinct rather than reason in order to survive.