Why do we smile when we are happy and cry when we are not feeling well? Why do we furrow our brows in doubt and widen our eyes in excitement? For many centuries, scientists have been interested in studying human facial expressions and wonder whether there are expressions common to all people or if they are tied to cultural backgrounds, and whether they are learned through constant repetition or are innate. Charles Darwin explores this in light of his hypothesis that all emotions are innate, and he further posits that animals express many emotions in ways similar to humans. In his work, first published in 1872, Darwin attempts to prove the universality and thus genetic basis of emotional expressions through meticulous observations.