"Where did Cain get his wife?"

Many ask this question thinking they’ve found a "mistake" in the Bible—that there must have been other people besides Adam and Eve. Scripture tells us that Adam is "the first man" (1 Corinthians 15:45); that there were no other humans when he was created, because God said, "It is not good that the man should be alone" (Genesis 2:18); and that Eve is "the mother of all living" (Genesis 3:20). Cain and Abel, then, must have married distant sisters. All of the first-generation siblings married each other in order to populate the earth. At that time there was no law against incest. But as the population grew large enough, and as the risk of genetic problems increased because of sin’s curse, God outlawed marriage between siblings.