In Book one, Chapter 68 of On the Merits and Forgiveness of Sins and on the Baptism of Infants St. Augustine posits that the prolonged helplessness of infancy is a penal result of Adam's fall. Had Adam not sinned perhaps infants would have grown much quicker. Augustine also compares the sustained helplessness of infants with the quick growth of animals.
The question which we are now discussing is not about Adam in respect of the size of his body, why he was not made an infant but in the perfect greatness of his members. It may indeed be said that the beasts were thus created likewise — nor was it owing to their sin that their young were born small. Why all this came to pass we are not now asking. But the question before us has regard to the vigor of man's mind and his use of reason, by virtue of which Adam was capable of instruction, and could apprehend God's precept and the law of His commandment, and could easily keep it if he would; whereas man is now born in such a state as to be utterly incapable of doing so, owing to his dreadful ignorance and weakness, not indeed of body, but of mind — although we must all admit that in every infant there exists a rational soul of the self-same substance (and no other) as that which belonged to the first man. Still this great infirmity of the flesh, clearly, in my opinion, points to a something, whatever it may be, that is penal. It raises the doubt whether, if the first human beings had not sinned, they would have had children who could use neither tongue, nor hands, nor feet. That they should be born children was perhaps necessary, on account of the limited capacity of the womb. But, at the same time, it does not follow, because a rib is a small part of a man's body, that God made an infant wife for the man, and then built her up into a woman. In like manner, God's almighty power was competent to make her children also, as soon as born, grown up at once.
But not to dwell on this, that was at least possible to them which has actually happened to many animals, the young of which are born small, and do not advance in mind (since they have no rational soul) as their bodies grow larger, and yet, even when most diminutive, run about, and recognize their mothers, and require no external help or care when they want to suck, but with remarkable ease discover their mothers' breasts themselves, although these are concealed from ordinary sight. A human being, on the contrary, at his birth is furnished neither with feet fit for walking, nor with hands able even to scratch; and unless their lips were actually applied to the breast by the mother, they would not know where to find it; and even when close to the nipple, they would, notwithstanding their desire for food, be more able to cry than to suck. This utter helplessness of body thus fits in with their infirmity of mind; nor would Christ's flesh have been
in the likeness of sinful flesh,unless that sinful flesh had been such that the rational soul is oppressed by it in the way we have described — whether this too has been derived from parents, or created in each case for the individual separately, or inspired from above — concerning which I forbear from inquiring now.
