That is one of the reasons. But I have yet to figure out why he thought that Adam's body was somehow changed when he ate of the forbidden tree:
"Our bodies would not have been born with defects, and there would have been no human monsters, if Adam had not corrupted our nature by his sin, and that had not been punished in his posterity. Op. Imp. I. 116; II. 123; III. 95,104; V. 8. The sickly and dying nature of the human body, proceeds from the lapse of the first man. De Gen. ad Lit. XI. 32" [emphasis added] (G.F. Wiggers, An Historical Presentation of Augustinism and Pelagianism From the Original Sources, 97).
Do you have any idea where he got that idea? Even John Calvin followed Augustine in that regard, writing that
"everything which is in man, from the intellect to the will, from the soul even to the flesh, is defiled and pervaded with this concupiscence; or, to express it more briefly, that the whole man is in himself nothing else than concupiscence" (John Calvin,
Institutes of the Christian Religion;2:1:8).
Perhaps someone knows why Augustine thought that the body of Adam was changed when he ate of the forbidden tree? It also seems that Calvin also followed Augustine in regard to his ridiculous ideas concerning concupiscence. Wiggers says that
"Augustine explains himself to this effect, that carnal concupiscence has its seat in the body as well as in the soul. 'The cause of fleshly lust is not in the soul alone, and still much less in the body alone. For it arises from both; from the soul, because without it no delight is felt; and from the flesh, because without this, no fleshly delight is felt,' etc. X. 12." [emphasis added] (
Ibid., 95).
According to Augustine before Adam and Eve fell they had no fleshy lust (concupiscence):
"Before the fall, and before there was any necessity of dying, concupiscence had no existence; but after the body had acquired a sickly and dying nature, (which likewise belongs to the flesh of animals), it received also, on this account, the movement by which the carnal desire originates in animals, whereby those that are born, succeed the dying.' De Gen. ad Lit. XI. 32" [emphasis added] (Ibid.).
Frankly, it is hard for me to take anything which Augustine says seriously.