In the Bible, where did Cain get his wife?
This question is often asked by those who are attempting to find problems with the validity of the Bible or it could occur with someone who is simply trying to figure out how it could occur, but usually the former is more common. To understand the reasons for what is about to be explained, it is important to understand a few important aspects.
Throughout the Bible, geneaology plays an important role in understanding the line of the Jewish people for the sake of the Messiah, Jesus Christ (ultimately), and for the purpose of demonstrating God's desire for Israel to keep themselves separate from the pagan nations and not to intermarry with people from the other nations. God's desire is for all people to be saved, but He chose Israel as a nation for Himself and to be an example and is displayed throughout the writings of the Old Testament.
Given the importance of geneological history, it is important to note that such history was provided with male naming and accounting purposes and did not typically include the name of a wife. Typically, we see the mention of male descendants of the father. We do not typically see the mention of daughters, but there are a few exceptions. Given this, it would be typical to provide the male descendants and not the females (daughters).
To put it simply, the female descendents of Adam and Eve we not detailed, but the males are described and this keeps with the typical geneological history that the Bible uses throughout. Therefore, we can reliably rest in the idea that Cain would have taken one of his sisters as a wife.
Do we have any proof to the fact that Adam and Eve had daughters as well as sons? In fact, there is evidence to this fact as described just a few chapters later in the Bible from the following verse:
“After he begot Seth, the days of Adam were eight hundred years; and he had sons and daughters.” (Genesis 5:4, NKJV)
If you wonder if this reference could be talking about Seth having son's and daughters, it actually mentions Seth's family lineage and uses the same reference to him having "sons and daughters" as well. Therefore, it would be redundant to say the same thing a few verses later. Therefore, this reference here in Genesis 5:4 refers to Adam having "sons and daughters."
Perhaps you are wondering if this presents a problem with the prohibitions against incest. Well, we have to realize that sin was not as pervasive and the prohibition not to marry within the family was not given until later on in the Bible. Therefore, God's prohibition of marrying within the family (incest) was not specifically given at the time Cain would have taken his wife. In addition, the concept that sin would have been less and less pervasive is also an interesting point of consideration as to why the prohibition against incest would be given later. Given the impact of sin over time, the prohibition of incest and the resulting impact of it would now have risen to a level whereby God put a prohibition on it to prevent the problems caused and evidenced by what we can see within inbreeding. To clarify, inbreeding could occur while sin was less pervasive without complications. Once God's prohibition was in place against incest, there was then a clear prohibition against it.
There would be no reason to reject the Bible as being untrue based on this question. There is no reason to be concerned that there is no answer for where Cain got his wife. He simply married one of his sisters and the reliability of the Bible is maintained.
Thanks to Answers in Genesis ministry with helpful insights gleaned from their DVD resources.