Is every human being descended from Adam and Eve, including Abraham?
Yes. The biblical account presents Adam and Eve as the first and only created humans, forming one original race. From them came all people, including Abraham, who lived about 2,000 years later. After Noah’s flood, the human race continued through Noah’s three sons and their wives, and Abraham descended from Shem’s line.
Les explains that from the creation of Adam there was one race of people, and everybody—including Abraham—comes from Adam and Eve. He addresses the question of Cain’s wife by saying there certainly were no other people, because only Adam and Eve were created. Thus brothers married sisters for the first generation or two, and that was no problem because the human race was still so pure genetically. He notes that even Abraham, 2,000 years after Adam, married a half-sister with God’s blessing, and there was nothing wrong with Isaac. God did not put a taboo on marrying close relatives until sometime after Abraham, because by then the genetic pool was weakening. After Noah’s flood destroyed all except those in the ark, the human race began again through Noah’s three sons and their wives, and Abraham came out of the line of Shem.