1. Whom Did Cain Marry?

In Genesis 5:4 we are told that after Seth was born, Adam had other sons and daughters. The assumption, therefore, is that Cain married one of his relatives, either a sister, cousin, or niece. Although this seems odd, who else would there have been for him to marry?

We have an example in the Bible of someone else being married to his half-sister: Abraham. (see Gen. 20:9-13)