Final answer:
St. Augustine proposed the "realistic" theory of original sin stating that humanity was seminally present in Adam when he sinned, implicating all humans in his transgression and inheriting the nature of sin.
Step-by-step explanation:
The "realistic" theory (Original sin) of sin was proposed by St. Augustine and stated that we were seminally present in Adam when he sinned. According to this view, all of humanity is implicated in Adam's transgression since they were, in a real sense, present in him. This directly relates to the idea of original sin, where the human nature of having a tendency to sin is inherited from our first parents, Adam and Eve. St. Augustine's view is that evil entered the world because of their disobedience in the Garden of Eden and consequently, humanity bears the consequences. This concept poses philosophical questions about the nature of God's omniscience and benevolence, and the presence of evil in the world.