I agree that transmission of Original Sin cannot be explained biologically.
However, Augustine’s view deserves closer attention.
It is well known that Augustine aimed to refute Pelagianism, a doctrine that overestimates the power of human will and considers humans capable of Salvation without the help of God’s Grace; according to Pelagius the bad influence of Adam on his descendants is that of bad example. Before Augustine the Church Father Irenaeus of Lyon had to struggle against Gnosticism, a doctrine that considers human nature completely depraved and human flesh inherently sinful; in this perspective human free-will becomes abolished in the end.
The scriptural basis for the teaching of “Original Sin” is: Psalm 51:7, John 3: 5, and St. Paul’s letters. On this basis the Greek Fathers with Irenaeus, and later Augustine basically highlighted two things:
All humans are in need of Redemption, even if they have not personally sinned.
Human will is really free and therefore the fact that each human person needs God’s Grace to be saved does not imply that each person has to sin.
For the sake of explanation Irenaeus coined the concept of “Original sin”. And Augustine elaborated further on it stating that Original Sin is transmitted by propagation and not by imitation (“bad example”).
Since at that time there was no ground to doubt the literal interpretation of the Genesis narrative that all humans are biologically descended from a single couple, Augustine’s explanation (“On Merit and the Forgiveness of Sins, and the Baptism of Infants-Book I”) became coupled to the biological reproduction and more recently to genetically transmission. In this line of thinking some awkward conclusion was derived, as for instance Thomas Aquinas’s claim that “if Eve, and not Adam, had sinned, their children would not contract original sin” (S.Th. I-II, q. 81, a.5).
So we have to distinguish four claims:
A): Each person is free NOT to sin.
B): The very fact of Redemption by Jesus Christ implies that each human person is generated in the stage of “being in need of Redemption through Jesus Christ’s Grace”.
C): The fact of “being in need of Redemption” (called “stage of Original Sin”) is caused by the first sin committed in human history.
D): The stage of “Original Sin” is linked to biological descent from a single couple.
A), B) and C) are the main assumptions of the Fathers and Doctors of the Church (Greek Fathers, Irenaeus, Ambrose, Augustine, Thomas Aquinas among others), and is the actual content of the Decree on Original Sin of the Council of Trent.
It is important to stress that the reason for C) is not that Augustine
C) is in fact a consequence of A) and B):
The stage of “being in need of Redemption” (“Original Sin”) can neither be explained by assuming that each person necessarily sins [against A)], nor through sins of other persons (ancestors or contemporaries) different from the first sin in human history.
The stage of “being in need of Redemption” cannot be explained invoking Adam’s “representation of mankind” either:
Such an explanation implies that if Adam (“God’s representative”) had not sinned and sin had arrived generations after Adam, humans would not have been in need of Redemption.
D) is an unhappy claim that actually is not implied by A), B), and C), and even Pope Pius XII claims that it has to be maintained only as far as one cannot explain A), B) and C) otherwise.
Evolution is teaching us that we have to give up D), and thereby is helping us to make better theology: We can maintain A), B) and C), and search for a suitable explanation. My proposal is that Romans 11:32 provides the key for achieving this.
After this discussion I would be thankful to know your position regarding the three Premises A), B) and C) above:
Do you accept or reject them?
As in other points your answer will surely help us to progress.