“Reuben was the first-born of Israel. However, because he defiled his father’s bed, his birthright was given to the sons of Joseph the son of Israel. Thus Reuben is not enrolled in the genealogy according to the birthright.”
Now we are going to look at the Transjordan area or the east side of the Jordan River. First up is Reuben, who was technically the first born child of Jacob or Israel. Leah, the older sister of Rachel was the mother of Reuben and 5 other sons of Jacob. In Genesis, chapter 35, Reuben had sex with his father’s concubine, Bilhah, who was actually the mother of his step brothers, Dan and Naphtali. Thus he had sex with his step mother while Israel was away. There was no indication in Genesis that Israel took the birthright away from Reuben to give it to the sons of Joseph. The only indication is that Jacob, on his deathbed made the sons of Joseph his, just like Reuben and Simeon in Genesis, chapter 48. There was no talk of replacing them, just making them equal. In fact in Genesis, chapter 46, the biblical author when listing those who went to Egypt with Jacob, listed Reuben first with his children.