Where Did Cain Get His Wife?
Jon Gary Williams
Then Cain went out from the presence of the Lord and dwelt in the land of Nod on the east of Eden. And Cain knew his wife, and she conceived and bore Enoch. And he built a city, and called the name of the city after the name of his son, Enoch. (Genesis 4:16-17)
The scriptures provide no information regarding Cain's wife. We are not told her name and we're not given any details on what family she was from.
Some have ventured to say that God created an entirely separate group of people, not from the lineage of Adam, and from this family came the woman who became Cain's wife. While God certainly could have done so, this was not the case, for the Bible is clear in stating that Eve was "...the mother of all living" (Genesis 3:20).
The obvious answer to this question is that Cain married one of his relatives - a sister or possibly a niece. We are not told how many years passed between the births of Cain and Able until the time Cain murdered of Able and went to Nod. There could have been many years during which Adam and Eve had other children, given the fact that Adam and Eve had been told, "Be fruitful and multiply and replenish the earth..." (Genesis 1:28). So there could have been any number of women (sisters or nieces) from which Cain could take as his wife.
Some have argued that this could not be for it would involve an incestuous relationship. However, this overlooks that in the early stages of human reproduction man no doubt experienced a pure genetic state before harmful genetic traits existed. For example, we read that even at the time of Abraham he married his half-sister Sarah (Genesis 20:12).
Marriages between relatives was not an issue until many years later when it was outlawed under the Law of Moses (Leviticus 18). Through the years man's genes became contaminated, and to protect the nation of Israel God condemned incestuous marriages.