How is the theme of humanity shown though Shakespeare's play Othello?

All of Shakespeare's plays deal with core human emotions and the effect they have when they are misunderstood, manipulated and used for personal gain. That fact has not changed through the centuries, and nor has the human need for community and acceptance, the basic tenets of humanity. There are plenty of people who recognize that need and take advantage, and Othello is particularly vulnerable as he feels like an outsider. He constantly tries to prove himself or show his worth. While having to justify his marriage to Desdemona, having been accused of using "witchcraft" on her, he tells the Duke, in Act I, scene iii that Brabantio (Desdemona's father) "loved me, oft invited me, / Still questioned me the story of my life" (128) and yet now Brabantio is the one who has been manipulated by Iago into believing that Othello has "abused, stolen from me, and corrupted, by spells and medicines..." (60) his daughter. Human nature is such that people often act first and think later, with dire consequences.

Othello knows that Desdemona "loved me for the dangers ..." (167), and as he says in Act III, scene iii, "she had eyes and chose me" (193). However, he still worries that, because he is "black / And has (have) not those soft parts of conversation..." (267) that he may in some way be responsible if she has done what Iago is suggesting and been unfaithful to him with Cassio. Iago abuses Othello's humanity, his trust, his kindness and his goodwill, but still Othello does not recognize it, thinking "honest Iago" is trying to protect him. Othello does believe in Desdemona, but he unwittingly gives Iago another opportunity to intensify any doubts he may have. When Othello demands "ocular proof," (364), this creates the perfect opportunity for the unscrupulous Iago.

As soon as Othello has his proof, the fact that he believes that the only way to save Desdemona, and rescue his own self-worth and honor, is to kill her reveals an age-old human failing as control and power become the driving force behind Othello's actions. For Othello to believe that there can be such a thing as an "honorable murderer" (V.ii.297), and that his contribution to the Venetian state should mitigate the opinion of others, seals the pure tragedy of Othello and supports the theme of humanity.