Genesis 4:17 Updated American Standard Version (UASV)
17 Cain had sexual relations[1] with his wife and she conceived, and gave birth to Enoch; and he built a city, and called the name of the city Enoch, after the name of his son, Enoch.
Genesis 3:20 Updated American Standard Version (UASV)
20 Now the man called his wife’s name Eve, because she was the mother of all living.
Here we are just setting up the situation, and as you can see, all humans came to be the offspring of Adam and Eve.
Genesis 5:3-4 Updated American Standard Version (UASV)
3 When Adam had lived one hundred and thirty years, he became[2] the father of a son in his own likeness, according to his image, and named him Seth. 4 Then the days of Adam after he became the father of Seth were eight hundred years, and he had other sons and daughters.
As you can see, aside from Cain and Abel, there was Seth, as well as “other sons and daughters.” Therefore, one of Adam’s daughters must have married Cain. In fact, they lived for centuries; it could have even been his niece. We must keep in mind that these are the immediate descendants of Adam and Eve; therefore, they would have been closer to perfection. Their condition of good health would be far beyond the healthiest person living today; so, there would have been no chance of passing on defects, as would be the case even in the Time of Abraham, when they were still living almost 200 years. This is the reason you find Jehovah God forbidding incest 2.500 years later in the Mosaic Law.
Genesis 4:16-17 Updated American Standard Version (USV)
16 Then Cain went out from the presence of Jehovah, and dwelt in the land of Nod,[3] east of Eden.
17 Cain had sexual relations[4] with his wife and she conceived, and gave birth to Enoch; and he built a city, and called the name of the city Enoch, after the name of his son, Enoch.
Please note that Cain met his wife before he fled to another land. She was not from some other family. However, it was there that they had relations, and fathered a son.
Facts about Cain and his family
All humans descended from Adam and Eve. God “from one man [Adam] every nation of mankind to live on all the face of the earth.” (Acts 17:26) Adam’s wife, Eve, became the mother of all living.” (Genesis 3:20) Therefore, Cain must have married a descendant of Adam and Eve.
Cain and his brother Abel were the first of many children born to Eve. (Genesis 4:1, 2) When Cain was banished for killing his brother, he complained: “Whoever finds me will kill me.” (Genesis 4:14) Who was in existence at that time that should make Cain afraid? The Bible says that Adam “And the days of Adam after he fathered Seth were eight hundred years. And he fathered sons and daughters.” (Genesis 5:4) Evidently, these other descendants of Adam and Eve could have posed a threat to Cain.
Early in human history [Adam to Moses’ day], marrying one’s relative was a common practice. Abraham, for example, married his half sister, Sarah. (Genesis 20:12) The first forbidding such a marriage appeared in the Mosaic Law, which was written 2,500 years after Cain’s day. (Leviticus 18:9, 12, 13) Children born to close relatives after the flood were not as affected by birth defects because they were closer to human perfection. Abraham lived 175 years. People before the flood commonly lived over 900 years.
The Bible presents detailed genealogies going back to Adam in the book of Genesis, but also in the writings of the historians Ezra and Luke. (Genesis 5:3-5; 1 Chronicles 1:1-4; Luke 3:38) Bible authors give us the account of Cain as a historical event.—Hebrews 11:4; 1 John 3:12; Jude 11.
THESE ARE ALL BIBLICAL HISTORICAL REASONABLE, RATIONAL FACTS.
PRE-ADAMITES (e.g., R. A. Torrey, Gleason L. Archer Jr., John Stott, Hugh Ross)
Frank Turek, the late John Stott, and others have driven off the path of evangelical hermeneutics into a Jurassic Park movie, and they are not alone. My goodness. This is not inferencing, it isn’t even speculation, it is pure fantasy.
THE FALSE DOCTRINE OF PRE-ADAMITES: Was There Other Humans and Death Before Adam and Eve?
[1] Lit knew
[2] Lit begot
[3] That is, wandering
[4] Lit knew