Q. Where did Cain get his wife?
A. This question arises because most people assume that Adam and Eve had only three children: Cain, Abel, and Seth. Therefore, some people think that Cain must have found his wife from among some other family of humans. But the Bible says that all people come from Adam and Eve (see Genesis 3:20). Although the Bible specifically names Cain, Abel, and Seth as Adam and Eve’s children, it says that they had other children. In Genesis 5:4, we read, “And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters.” Some have assumed that this verse means that Adam had the other sons and daughters after Seth, but there is nothing in the wording of this verse that implies this. In other words, Adam and Eve had many other children throughout their long married life, both before and after the birth of Seth (Adam lived 930 years and God had commanded Adam and Eve to “be fruitful and multiply”—Genesis 1:28). For the sake of not competing for grazing, hunting, and tillable land, they would have spread over a large area. It is to these members of his family that Cain went and found a wife. Of course, this also applied to Seth.
Some see this as a problem because it means that Cain and Seth married close relatives, which these people see as sinful. But we know that Abraham married his half sister (Genesis 2:12). It was not until the time of Moses that God gave Israel laws prohibiting marriage between close relatives (see, for example, Leviticus, chapters 18-20). Therefore, it would not have been wrong for Adam’s sons to marry their close relatives, including even their sisters.