Augustine and Creationism: the Fecundity of the First People
City of God - Book 15, Section 15
Augustine provides further argumentation that the names mentioned in the Genesis genealogies may be only a tiny handful of all the children that were born. The argument involves the age of the parents and the length of time between births. Seth, for instance, was 105 years old when his son Enos was born. Augustine is incredulous that anyone could abstain from sex or remain childless for such long amounts of time.
Whether it is credible that the men of the primitive age abstained from sexual intercourse until that date at which it is recorded that they begat children.
Some one, then, will say, Is it to be believed that a man who intended to beget children, and had no intention of continence, abstained from sexual intercourse a hundred years and more, or even, according to the Hebrew version, only a little less, say eighty, seventy, or sixty years; or, if he did not abstain, was unable to beget offspring? This question admits of two solutions. For either puberty was so much later as the whole life was longer, or, which seems to me more likely, it is not the first-born sons that are here mentioned, but those whose names were required to fill up the series until Noah […].Further, when Seth was born, the age of his father is mentioned; but already he had begotten other sons, and who will presume to say that Cain and Abel were the only ones previously begotten? For it does not follow that they alone had been begotten of Adam, because they alone were named in order to continue the series of generations which it was desirable to mention. For though the names of all the rest are buried in silence, yet it is said that Adam begot sons and daughters; and who that cares to be free from the charge of temerity will dare to say how many his offspring numbered? […] [Regarding Seth and Enos], who but a rash man could affirm that this was his first-born? Will any man do so to excite our wonder, and cause us to inquire how for so many years he remained free from sexual intercourse, though without any purpose of continuing so, or how, if he did not abstain, he yet had no children?
Consequently it does not at all appear whether he who is named as the son was himself the first begotten. Nay, since it is incredible that those fathers were either so long in attaining puberty, or could not get wives, or could not impregnate them, it is also incredible that those sons were their first-born. But as the writer of the sacred history designed to descend by well-marked intervals through a series of generations to the birth and life of Noah, in whose time the flood occurred, he mentioned not those sons who were first begotten, but those by whom the succession was handed down.
In my opinion, there is one possible flaw or exception with Augustine’s reasoning here. Noah was 500 years old before he fathered Shem, Ham, and Japheth. That’s a long time to remain celibate --- perhaps for most of his life he was a social outcast or an “Omega”. And if he had other children besides these three beforehand, it is strange that the narrative makes no mention of them.