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.