In 1623, Hernando Ruiz de Alarcón, a parish priest in Atenango, Mexico, was commissioned by his archbishop to record Nahua beliefs and healing practices for the purpose of denouncing their superstitions and demonic magic. His "Treatise on the Heathen Superstitions That Today Live Among the Indians Native to This New Spain," 1629 underscores Spanish prejudice against diversity in religion, preserves the idolatrous and magical practices it discredits, and reveals the author's colonial mindset. Raised in the same restrictive Spanish colonial environment, Hernando's brother Juan was classically trained in Civil and Canon law. He became one of the major authors of the Spanish Golden Age, writing "comedias" that focused on loyalty, friendship, and honesty. His work often reveals a disparate view of magical practice. This article explores how applying epigenetics, the study of environmental influences on gene activation and its effects on physical and emotional behavior, to their circumstances can provide a tool for exploring their sibling differences in relation to magic. Colonial Mexico, Spain, the Catholic religion, the university, and personal physical challenges acted on genetic factors to form the essential nature and works of Hernando and Juan Ruiz de Alarcón.