The land of Nod was where Cain settled after he was punished by God for the murder of his brother Abel (Genesis 4:8). “And Cain went out from the presence of the Lord, and dwelt in the land of Nod, on the east of Eden.” Genesis 4:16.
No one knows where the land of Nod was located, only that it was east of Eden. The Bible does not mention the land of Nod again.
Cain’s settling “east of Eden” implies that he was further removed from the garden than Adam and Eve were. His fate was to live the life of an outsider. The fact that Cain left God’s presence suggests that he lived the rest of his life alienated from God.
The word Nod, in Hebrew, means “wanderer, exile, or fugitive.” This corresponds to God’s word to Cain.. “When thou tillest the ground, it shall not henceforth yield unto thee her strength; a fugitive and a vagabond shalt thou be in the earth.” Genesis 4:12
Though God had driven Cain from his home, it was Cain’s choice to live outside the presence of God. Essentially, Cain’s punishment in becoming a wanderer and a fugitive was to lose all sense of belonging and identification with a community. Living in the “land of Nod,” Cain lived without roots in isolation. For his sin, Cain was made a castaway and later became a godless, hollow person “in the land of Nod.” Upon separating himself from God, Cain built a society totally detached from God. The Bible tells us that the children of Cain followed in his path and established a godless civilization (Genesis 4:16-24).
The Bible does not specifically say who Cain’s wife was. The only possible answer is that Cain’s wife was his sister or niece or great-niece, etc. The Bible does not say how old Cain was when he killed Abel (Genesis 4:8). Since they were both farmers, they were likely both full-grown adults, possibly with families of their own. Adam and Eve had given birth to more
children than just Cain and Abel at the time Abel was killed. They definitely had many more children later.
“And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters:” Genesis 5:4
The fact that Cain was scared for his own life after he killed Abel (Genesis 4:14) indicates that there were likely many other children and perhaps even grandchildren of Adam and Eve already living at that time. Cain’s wife (Genesis 4:17) was a daughter or granddaughter of Adam and Eve.
Since Adam and Eve were the first (and only) human beings, their children would have no other choice than to intermarry. God did not forbid inter-family marriage until much later when there were enough people to make intermarriage unnecessary (Leviticus 18:6-18). The reason that incest today often results in genetic abnormalities is that when two people of similar genetics (i.e., a brother and sister) have children together, there is a high risk of their recessive characteristics becoming dominant. When people from different families have children, it is highly unlikely that both parents will carry the same recessive traits. The human genetic code has become increasingly “polluted” over the centuries as genetic defects are multiplied, amplified, and passed down from generation to generation. Adam and Eve did not have any genetic defects, and that enabled them and the first few generations of their descendants to have a far greater quality of health than we do now. Adam and Eve’s children had few, if any, genetic defects. As a result, it was safe for them to intermarry.