Genesis 25

I seems to me the story of Esau and Isaac if the first time in the Bible that we come upon the doctrine eof "birthright".

In the LDS Bible Dictionary we learn of the "birthright" -

Under the patriarchal order, the right or inheritance of the firstborn is known as birthright. This generally included a land inheritance as well as the authority to preside. The firstborn of flocks and of human families was considered as belonging to the Lord, and was expected to be dedicated to him. This dedication could be either literal or by the payment of redemption money (Ex. 13:11–16).

"From time to time certain prerogatives, opportunities, and blessings have attended those who were born of a particular lineage. Thus the office of high priest (of the Aaronic order) and the office of the patriarch to the Church (in the Melchizedek Priesthood) are hereditary in nature. Lineage alone does not guarantee the blessings or spiritual power of the office, but the opportunities are offered to the firstborn of the selected lineage. There are several instances in the scriptures of the one who was the firstborn losing his birthright because of unrighteousness, and his office being given to another; such is the case with Esau (Gen. 25:24–34; 27), and Reuben (1 Chr. 5:1–2; Jer. 31:9)." (Bible Dictionary | B Birthright:Entry)

Obviously, there was great responsibility with the birthright and not every "firstborn" was willing to honor and take on this responsibility.  It appears to me that the birthright extended beyond just spiritual things.  It appears to me the responsibility and obligation to take over the parents business or occupation and provide life ending care.  Not everyone would want to do that.  Thus the birthright could be extended down the line.

Obviously, the Lord can easily control the desire order of birth.  Yet at the same time, he provides opportunities for many to choose the right or choose an alternate course.  I find it interesting in Rebekah's case, as she was pregnant that -

"...the children struggled together within her; and she said, If it be so, why am I thus? And she went to enquire of the LORD.
23 And the LORD said unto her, Two nations are in thy womb, and two manner of people shall be separated from thy bowels; and the one people shall be stronger than the other people; and the elder shall serve the younger."  (Old Testament | Genesis 25:22 - 23)

By revelation, the Lord told Rebekah that the younger would assume the birthright.  As the Lord understood, even giving Esau the opportunity, that he would take this responsibility lightly for read that as -

"...Jacob sod pottage: and Esau came from the field, and he was faint:
30 And Esau said to Jacob, Feed me, I pray thee, with that same red pottage; for I am faint: therefore was his name called Edom.
31 And Jacob said, Sell me this day thy birthright.
32 And Esau said, Behold, I am at the point to die: and what profit shall this birthright do to me?
33 And Jacob said, Swear to me this day; and he sware unto him: and he sold his birthright unto Jacob.
34 Then Jacob gave Esau bread and pottage of lentiles; and he did eat and drink, and rose up, and went his way: thus Esau despised his birthright."  (Old Testament | Genesis 25:29 - 34)

Because Jacob would righteously honor this birthright, the great and promised blessings followed his posterity.