The answer I have usually heard from Biblical literalists is that they married their sisters (Adam and Eve also had daughters, according to Genesis 5:4).
It's a touchy subject, but facts are facts; and the Biblical Garden of Eden story involves incest.
Completely disgusting. I wish I did not know this. What a tragedy. I thought people had morals in the Bible. I went to 13 years of Catholic School and NEVER heard of this depravity. Are you sure?????
At the time their genetic codes were considered perfect enough that intercourse with close relatives did not produce the abnormalities seen later in history.
Mixing of the gene pool is what maintains human health and longevity.