Where Did She Come From?
Cains wife raises questions about the accuracy of the Bible. "Where did Cain get his wife?" is an old question, sometimes considered unanswerable by the skeptics. If one takes the early chapters of Genesis literally, it is supposed that Adam and Eve, and their two sons, Cain and Abel, were the only four people on earth. Where then did Cain's "wife" of Genesis 4:17 come from?
First, it is important to note that the details provided in the early part of Genesis are sketchy. Chapters 1-11 skim over several thousand years, with only as much information included as the Lord deemed necessary for us to have.
Chapter 4 speaks of three specific sons of Adam and Eve: Cain, Abel (whom Cain murdered), and Seth. We are given more detail on these, as both their spiritual history and their descendants prove to be significant later on. But these three were not the only children of Adam and Eve. We learn from Chapter 5 that Adam lived to the age of 930, and "had sons and daughters" (vs. 4-5). He and Eve could easily have had dozens of children in that time.
The existence of Cains wife is not the mystery it seems. All that was necessary for Cain to have a woman to marry is for at least two of Adam's children to marry each other and have children of their own. Perhaps Cain married a sister too, we do not know. And we are not told how long Cain lived. But if he lived to be over 900 years of age, as his brother Seth did (Gen. 5:8), there could well have been many generations of the family born during that time.
Today, there are civil laws prohibiting siblings from marrying. However, in the beginning the Lord apparently permitted it, in order to get the population started. It was only with the giving of the Law to Israel around 1400 B.C. that a man was forbidden from marrying his sister or other close relation (Lev. 18:6, 9--where the "one flesh" sexual aspect of the relationship is euphemistically described as "uncovering the nakedness" of the woman).
We know that today the intermarriage of family members can be genetically dangerous, as it can pass on various birth defects. However, in the early years following creation, the genetic pool was uncontaminated and there was no specific health reason for the restrictions that came later. (This is also likely part of the reason why people lived much longer in the beginning.) An all-wise Creator knew when to introduce limitations, and just what they should be.