The resounding theme of The Hairy Ape is the effect of industrialization and technological progress on the worker. Industrialization has reduced the human worker into a machine. The men are programmed to do one task, are turned on and off by whistles, and are not required to think independently. Today, the job of the coal stoker is actually done by a machine. Workers are thus forced into jobs that require nothing but grunt work and physical labor, which has, in turn, caused a general deterioration of the worker into a Neanderthal or Ape- like state. This is made clear by O'Neill's stage direction, which indicates that the Firemen actually look like Neanderthals and one of the oldest workers, Paddy, as "extremely monkey-like." The longer the Firemen work, the further back they fall on the human evolutionary path—thus Paddy, one of the oldest, is especially "monkey-like." As a whole, the play is a close investigation of this regressive pattern through the character Yank—the play marks his regression from a Neanderthal on the ship to an actual ape at the zoo.
Mildred and Yank are representative of the highest and lowest societal classes—as Long would term it, the bourgeois and the proletariat. However, while Mildred and Yank's lifestyles are extremely different, they share similar complaints about class. Mildred describes herself as the "waste product" of her father's steel company. She has reaped the financial benefits of the company, but has felt none of the vigor or passion that created it. Mildred yearns to find passion—to touch "life" beyond her cushioned, bourgeois world. Yank, on the other hand, has felt too much of the "life" Mildred describes. Yank desires to topple the class structure by re-inscribing the importance and necessity of the working class. Yank defines importance as "who belongs."
Class limits and determines both Mildred and Yank's financial resources, educational opportunities, outlook on life, and culture. The Hairy Ape reveals how deeply and rigidly class is inscribed into American Culture and the cultural and financial boundaries it erects.
The motif and idea of who "belongs" and the idea of "belonging" are continually reinforced throughout The Hairy Ape. Yank equates "belonging" with power and importance and uses "belonging" as a way to reverse societal power structures. In Scene One, Yank claims that he "belongs" to the ship, as opposed to the passengers in first class who are merely "baggage." Yank also associates "belonging" with an individual's usefulness and functionality. The firemen "belong" because they make the ship run and are essential to its workings.
Yank is especially affected by Mildred because she presents a world and class which he cannot belong to. After their meeting, the play essentially follows Yank in his quest to find belonging, finally leading him to the monkey- house at the zoo.
For Yank, thought is the ultimate boundary. Whether pressing his fingers to his head or sitting in the position of Rodin's "The Thinker," he cannot muster enough thought to make sense of or come to peace with the world around him. Thought only becomes necessary for Yank after he encounters Mildred in the stokehole. Mildred and he class present a new threat that Yank cannot eliminate or get rid of by physical might. Yank is forced to think how he can defend himself. This transition is exemplified in the "tink" joke among the men. Before Mildred enters the stokehole Yank finds thinking ridiculous and unnecessary, he laughs when he tells the other men he is "trying to tink." However, after the encounter, Yank earnestly tells the men that he is trying to "tink." When they joke and correct him in a mocking chorus, "Think!," he is genuinely hurt.
Yank's inability to think not only reveals his regression to a lower animal form, but also renders him unable to adapt to or defend himself in the world beyond the ship.
Yank's idiosyncratic speech, characterized by chopped and mangled words eliminate the possibility of Yank's successes or acceptance in a world or class other than his own. His deformed language makes real communication impossible. Ann Massa in "Intention and Effect in The Hairy Ape" puts it quite beautifully, "Yank can only break the bounds of his vocabulary and his style in the same violent and ultimately frustrated way that he bends the bars of his cell he can't break the mould of the apparently flexible yet imprisoning medium that is language and that is life." Yank's speech defines his class and place in society—rigid, unchanging and binding.
The settings and environments of The Hairy Ape reveal larger social and cultural realities. Yank and the Firemen exist within the cramped and hot forecastle and stokehole, described as a formidable cage. In contrast, Mildred and her Aunt's environment, the Promenade Deck of the ship, is filled with fresh air and sun. The ocean that surrounds them is infinitely spacious and the general feeling of freedom abounds. The promenade deck is also symbolically situated above at the top of the ship, far above the stokehole. Both the stokehole and the promenade deck setting epitomize the lifestyles and characteristics of the ship's literal decks and subsequent upper and lower classes aboard.
Yank's impression of Rodin's statue, "The Thinker" is symbolic of Yank's need to think. While he physically embodies the cultural symbol of a "thinker" he cannot think himself. Every time O'Neill's stage direction calls for the actor to take the position of "The Thinker" Yank has come up against an obstacle that cannot be tackled by any other means but thought—when Yank cannot process the realities before him. After Yank is thrown out of the I.W.W he immediately gets into "The Thinker" pose. He is desperate to make sense of his situation and understand why the union would throw him out
The real ape in Scene Eight is the only other character that takes "The Thinker" position. The ape sharing this habitual body position reflects on Yanks own animalistic state—his mode of thought is no more advanced than the ape's.
Apes are everywhere in The Hairy Ape: Yank is called an ape, Yank thinks he is an ape, Mildred thinks she sees an ape, Yank tells people he is an ape, Senator Queen writes that the Wobblies will degenerate American civilization "back to the ape" and, most importantly, there is a real live ape in Scene 8. The ape symbolizes man in a primitive state before technology, complex language structures, complex thought or money was necessary. The ape represents man that is not only behind in an evolutionary sense, but is free of class, technology and other elements of modern society. The ape is only concerned with survival.
Thus Yank, constantly compared with apes, does share some characteristics with his early primate relatives. Yank, like the ape, struggles with thought, doesn't understand the class system, has at best basic language skills and is most concerned with his survival on Earth. In addition, male apes are known to be very territorial, obstinate, bull headed and aggressive—all descriptors that could be used to describe Yank.
Steel is both a symbol of power and oppression in The Hairy Ape. While Yank exclaims in Scene One that he is steel, "the muscles and the punch behind it," he is all the while penned in a virtual cage of steel created by the ship around him. Steel creates other cages in the play—Yank's jail cell and the cell of the Ape. Steel is also oppressive because it creates jobs like Yank's, it is symbolic of the technology that force Yank and the Firemen into slave-like jobs.