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Question: What is the origin of the doctrine of original sin?
Question: What is the origin of the doctrine of original sin?
There is no evidence that the doctrine existed before Augustine
One non-LDS author observed:
The idea of ‘original sin’ has been so commonly identified with traditional Christianity that the rejection of the one has seemed to imply a rejection of the other. It is supposedly an unquestioned assumption of Christian soteriology. In truth, the teaching that all...men are guilty of Adam’s sin, that each person must pay the penalty for, as Augustine declared (De corrept. et grat., 28), is really the product of his legalistic and Neo-platonic imagination. No scholarly work, whether treating the Scriptures or the Fathers, has demonstrated…that the idea of ‘original sin’ belongs to ‘the faith once delivered to the saints’ (Jude 3) or ever existed before Augustine. The same may be said for his theories of Grace and Predestination which accompany it, all of which are the result of his ‘Neo-platonic world-view’ [quoting G. Nygren, ‘The Augustinian Conception of Grace,’ Studia Patristica 2 (1955): 260]. Many of his contemporaries opposed him [and] … were scandalized by his lack of traditionalism—and not without justification” (39). 
We learn, then, that:
- there is no evidence that the doctrine existed before Augustine
- Augustine's view drew on his legal training, and his background in Greek Neo-Platonism.
- there was great opposition to Augustine's views, because his concept of "original sin" was not the traditional Christian teaching, but a drastic novelty.
- Augustine's novel view of original sin led to alteration in other doctrine, such as his ideas on Grace and Predestination.
Part of Augustine's error can be explained by the fact that he did not read or speak Greek. He was forced, then, to rely on Latin translations of both the scriptures and the writings of other early Christians.
As Azkoul goes on to observe:
- The moralist problem concerning the transmission of guilt and death to the descendants of Adam which preoccupied Augustine made a traditional reading of the verse [Romans 5:12] impossible. He not only abused it, but the entire witness of St. Paul with its Hebraic background. Unfortunately, the Bishop of Hippo [i.e., Augustine] did not know Greek and depended on the Latin translation of the New Testament. It was Ambrosiaster who provided, perhaps unwittingly, with Romans 5.12 as a proof-text” (42). The Latin text was rendered: ‘Wherefore, as by one man sin entered into the world and death by sin, so death passed upon all men, for all have sinned.’ The correct translation from the Greek reads: ‘Wherefore, as by one man sin entered the world and through sin death; on account of death all have sinned’ (42-3). Neither Origen [whom Augustine read: CD xi. 23] or Ambrosiaster gave voice to the doctrine of ‘original sin.’…. Quite simply, then, Augustine strayed from the truth, the Apostolic Tradition, and any attempt to justify his innovations by an appeal to some questionable principle of historical interpretation—‘doctrinal development’—will not help“. 
On the need for infant baptism
Of the consequences of Augustine's mistake, Stephen Duffy writes:
“his [Augustine’s] interpretation [of Romans 5.12], mistaken as it was, and deriving from the erroneous Old Latin version, would play a crucial role in the development of the later doctrine of original sin.” Ambrosiaster, the name given to an anonymous late fourth century commentator on the writings of Paul “does not seem [to think that] we are punished for Adam’s sin, but for our own: ‘…We are not made guilty by the fact of birth, but by evil deeds’ [On Romans 5.12-14; Questions on the Old and New Testaments 21f]” (63)...
“While granting that the tragic fall-out from Adam’s sin has contaminated all, Greek Christianity negates any transmission of guilt from Adam to his posterity. And the Eastern anthropology is in general more optimistic than that of the West. The two Gregories [Nyssa and Nazianzus] and Chrysostom maintain that the newborn are free from sin and so they are unperturbed about children dying without baptism….
Gregory of Nyssa, e.g., asserts that sin is congenital and that even Christ’s humanity was prone to sin [hamartetiken]” (63). Didymus the blind (ca. 313-398), last head of the famous catechetical school of Alexandria, speaks of the sin of Adam in virtue of which all are under sin, which is transmitted, it seems, by the sexual union of their parents. This involuntary, hereditary sin calls for purification not punishment [On 2 Corinthians 4.17 and Against the Manichaeans 8]” (64). “All this falls short of the classical Augustinian doctrine of original sin but key elements of that doctrine were already taking shape, especially in the West” (64). 
LDS readers see this as clear evidence of the apostasy impacting Christian doctrine—the loss of the apostles led Augustine and others to try to resolve difficult issues. Augustine was influenced by his culture, his practice of law, and his philosophical neo-platonism. These led him and others to gradually alter Christian doctrine, and yet these alterations would snowball. Augustine's adoption of original sin led, logically, to the need to baptize infants—an idea totally at variance with earlier Christian practice and doctrine.
Effect on ideas of grace and predestination
One error (Augustine's view of original sin) led to other alterations to Christian doctrine, which previous generations would have found incomprehensible:
According to Augustine, ‘original sin’ precluded any human cooperation with the divine Grace…. The human will is powerless to choose the good by virtue of the evil inherited from Adam. Unable to choose, he must be drawn irresistibly to God by grace. Original sin and predestination are both innovations without support in the Tradition of the Church. 
Azkoul then translates from G.F. Wiggers, Versuch einer pragmatischen Darstellung des Augustinisimus und Pelagianismus (Hamburg 1821: 448):
“In reference to predestination the Fathers before Augustine were entirely at variance with him and in agreement with Pelagius…. No ecclesiastical author had ever yet explained the Epistle to the Romans (e.g., Rom. 5.12) as Augustine had…. It was only by a doubtful inference, too, that he appealed to Cyprian, Ambrose, Gregory of Nazianzus, etc….’” 
- Michael Azkoul, “Peccatum Originale: The Pelagian Controversy,” Patristic and Byzantine Review 3 (1984): 39.
- Azkoul, 43.
- Stephen J. Duffy, The Dynamics of Grace: Perspectives in Theological Anthropology (Collegeville, Minn.: Liturgical Press, 1993), 62-63.
- Azkoul, 40.
- Azkoul, 51, note 5.