One of the strongest arguments against the mainstream Creationist narrative (and perhaps the only significant argument I’ve ever encountered) is that the ideas and the questions posed by modern Creationists are very recent developments and that the ancient Christians did not wonder about the same sort of things. Indeed, it would be very strange if there were no record that the ancient Christians asked questions like “Where did Cain get his wife?” or “Why did the earth’s population explode so dramatically that there were cities full of people within Seth and Cain’s lifetime?” These are very obvious questions that would occur to anyone inclined toward interpreting the Genesis account as literal history.
If it were true that the Church Fathers did not address these sorts of questions, it would be a serious blow to the Creationist movement. It would mean that the common view among the early Christians was that that Genesis was a pure allegory.
As far as I can tell, however, this argument is false. Not only were the ancients asking the same sort of questions as the modern Creationists, in some ways they addressed the issues in much greater detail.
The City of God by Saint Augustine (AD 354–430) addresses a lot of Creationist ideas, particularly in Book 15. In Book 15, Section 8, Augustine addresses the population boom problem. Where did cities full of people come from so quickly? He explains that although Genesis only records the names of a few of the first children, there were likely many, many more whose names are not recorded. Only people of significance are mentioned by name. And he concludes that since people lived so long back then, it is reasonable to suppose that they had multitudes of children.
What Cain's reason was for building a city so early in the history of the human race.
At present it is the history which I aim at defending, that Scripture may not be reckoned incredible when it relates that one man built a city at a time in which there seem to have been but four men upon earth, or rather indeed but three, […] But they who are moved by this consideration forget to take into account that the writer of the sacred history does not necessarily mention all the men who might be alive at that time, but those only whom the scope of his work required him to name. […]
Therefore, although it is written, "And Cain knew his wife, and she conceived and bare Enoch, and he builded a city and called the name of the city after the name of his son Enoch," it does not follow that we are to believe this to have been his first-born; […] And though no one attained the age of a thousand years, several exceeded the age of nine hundred. Who then can doubt that during the lifetime of one man the human race might be so multiplied that there would be a population to build and occupy not one but several cities? […]
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Augustine, of course, is only one of the Church Fathers. I don’t know if any of the others wrote about these issues. Augustine himself records that there was some controversy around what he was saying. It is reasonable to conclude therefore that not all the early Christians interpreted Genesis literally --- a situation very similar to what we face today. Nothing really has changed in all this time.