Augustine of Hippo, On the Merits and Forgiveness of Sins, and on the Baptism of Infants I.69: The Ignorance and the Infirmity of an Infant

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.