"One face, one voice, one habit, and two persons!"

This thesis considers the relationship between scientific advances, identity formation, and literature in an early modern print culture. As medical theorists made their discoveries and defended their work they did so within the literary world; turning to the printed word to cultivate their personal identity and rebut dissenting colleagues. Subsequently, playwright William Shakespeare employed common medical knowledge within his plays. Twelfth Night presents male and female twins within the scope of a comedy that plays upon the issues of cross-dressing and mistaken sexual identity. During the Renaissance, it was believed that male and female seed was co-present in every person and through dominance a distinct sexual identity was developed. This thesis argues that while Shakespeare initially convoluted this by allowing one of the twins to cross-dress; he resolved the anatomical doubling by presenting both characters together on stage at the close of the play.