Not to affect many proposed matches
Of her own clime, complexion, and degree,
Whereto we see in all things nature tends –
Foh! one may smell in such a will most rank,
Foul disproportion thoughts unnatural.

– William Shakespeare

Othello, Act 3, Scene 3. Iago questions Desdemona’s decision to marry a black foreigner like Othello as something unnatural. She went against her nature by rejecting young men of her own country, her skin color and status, he claims. Iago suggests that this is a sign of Desdemona’s dark and unnatural thoughts. Speaking to Othello, he is playing on his insecurities as a black Moor married to a white Italian woman.