This question is often asked in order to argue that there may have already been a race of people on the earth before God created Adam and Eve. In the days of slavery and prejudice some used this as an argument for the origin of the black races. Others have used it to imply evolution having already taken place on the earth or even that Satan had created a race of people. The matter is settled with three simple facts:

Genesis 4:16-17 — Cain did not meet his wife when he went to the land of Nod, he had relations with her. He already had her when he went to Nod.

Genesis 3:20 — Eve is the mother of all living.

Genesis 5:4 — Adam and Eve had many sons and daughters. Cain, therefore, married a sister. This, however, was not a problem for two reasons:

  1. Mankind was genetically brand new and did not need to worry about the 1500 genetic defects that we have today in our gene pool.
  2. God did not forbid intermarriage until Leviticus 18 where the nearest of kin one was allowed to marry was first cousin.

Possibly related: