Original sin, also called ancestral sin, is the Christian doctrine of humanity's state of sin resulting from the fall of man, stemming from Adam's rebellion in Eden. This condition has been characterized in many ways, ranging from something as insignificant as a slight deficiency, or a tendency toward sin yet without collective guilt, referred to as a "sin nature", to something as drastic as total depravity or automatic guilt of all humans through collective guilt.
The concept of original sin was first alluded to in the 2nd century by Irenaeus, Bishop of Lyons in his controversy with certain dualist Gnostics. Other church fathers such as Augustine also developed the doctrine, seeing it as based on the New Testament teaching of Paul the Apostle (Romans 5:12–21 and 1 Corinthians 15:22) and the Old Testament verse of Psalm 51:5.Tertullian, Cyprian, Ambrose and Ambrosiaster considered that humanity shares in Adam's sin, transmitted by human generation. Augustine's formulation of original sin was popular among Protestant reformers, such as Martin Luther and John Calvin, who equated original sin with concupiscence, affirming that it persisted even after baptism and completely destroyed freedom.The Jansenist movement, which the Catholic Church declared to be heretical, also maintained that original sin destroyed freedom of will.