according to their birth
Exodus 1:1-4
1
Now these are the names of the children of Israel who came into Egypt; every man and his household came with Jacob:
2
Reuben, Simeon, Levi and Judah,
3
Issachar, Zebulun and Benjamin,
4
Dan and Naphtali, Gad and Asher.
Genesis 43:33
And they sat before him, the firstborn according to his birthright and the youngest according to his youth; and the men marveled one at another.