Q. The Bible only tells us that Adam and Eve had 3 sons. Where did the women come from for the sons to marry? Where in the Bible is that explained? I’m also thinking about the inbreeding that had to happen after the rain stopped and Noah and his family populated the earth. Doesn’t that mean there has to have been some physical and mental abnormalities in subsequent generations?
In response to your question about who Adam and Eve’s sons married, while the book of Genesis only narrates the birth of their three sons Cain, Abel, and Seth, a genealogy shortly afterward in the book says, “After Seth was born, Adam lived 800 years and had other sons and daughters.” Jewish tradition says that the sons of Adam and Eve married their sisters. This is also what we must infer from the Genesis narrative, since according to it they could not have gotten wives any other way.
Like the situation you noted of Noah’s sons’ children necessarily marrying their first cousins, this situation of Adam’s sons necessarily marrying their sisters raises the issue of whether “physical and mental abnormalities” resulted. I recall one of my professors in seminary addressing this issue. He said that because the human race was still so young in the time of both Adam and Noah, there had not been an accumulation of genetic weaknesses that would lead to such abnormalities. In other words, the human gene pool was clear and strong and it could overcome this risk. That is one possible explanation. Another is that to enable humans to “be fruitful and multiply” successfully, God granted the equivalent of divine healing in the form of good genetic health. We should note that the biblical text does not say either of these things explicitly, but they are ways in which we can try to understand the biblical story.
This post addresses a question related to yours:
Good Question 