Who is Cainan in Luke's genealogy, and why isn't he in Genesis?
Cainan appears between Arphaxad and Shelah in Luke 3:35–36 and LXX Genesis 11:12–13, but is absent from the Masoretic Text of Genesis 11. The LXX inserts him in at least four separate passages; the MT omits him in all four. Both traditions are ancient — a Dead Sea Scroll (4Q27) preserves a related reading.
If you read Luke's genealogy of Jesus carefully, you find a man who doesn't appear in the standard Hebrew Old Testament. Between Arphaxad and Shelah, Luke places a figure named Cainan:
τοῦ Σαλὰ τοῦ Καϊνάμ τοῦ Ἀρφαξὰδ τοῦ Σὴμ τοῦ Νῶε
"of Shelah, of Cainan, of Arphaxad, of Shem, of Noah" — Luke 3:35–36
The standard Hebrew text of Genesis 11:12 reads: "Arphaxad fathered Shelah" — no Cainan between them, no mention of him anywhere. So where did Luke get him?
Cainan appears in the ancient Greek translation of the Old Testament — the Septuagint — in at least four separate passages. LXX Genesis 10:24 inserts him between Arphaxad and Shelah. LXX Genesis 11:12–13 gives him a full genealogical entry with ages: he fathered Shelah at 130 years old and lived 460 years total. He also appears in 1 Chronicles 1:18 in some LXX manuscripts. Luke was following a Greek text tradition that included him.
The question this raises is which direction the difference goes. Either Cainan was added to four separate, independent passages in the Greek tradition, or he was removed from four separate passages in the Hebrew tradition. A single scribal slip doesn't propagate like that — whatever happened was systematic. Both the addition and the removal require intentional effort across multiple texts.
One possibility for the Hebrew removal: the Book of Jubilees (a pseudepigraphal text from the 2nd century BC, attested in 15 manuscript fragments at Qumran) includes Cainan and gives him a specific story — he found pre-flood inscriptions containing forbidden astronomical knowledge from the Watchers and copied it in secret (Jubilees 8:3–4). As Second Temple Judaism moved away from Enochic traditions in the late period, a patriarch whose defining act was preserving angelic forbidden knowledge may have become theologically inconvenient. But that is inference, not proof.
What is not inference: Luke 3:36 includes Cainan (G2536), meaning Luke followed a text tradition that had him. Both the "presence" and "absence" readings are ancient. This is a genuine textual complexity, not an error in Luke.
Could Abraham have met Noah? Did they overlap?
According to the Masoretic Text's genealogical numbers, Noah died when Abraham was 58 years old — they were contemporaries. The Septuagint's numbers place 722 years between Noah's death and Abraham's birth. The two oldest witnesses give contradictory answers.
Did the Masoretic Text or the Septuagint change the patriarchal ages in Genesis?
The external evidence favors the MT reducing the numbers rather than the LXX inflating them. Demetrius the Chronographer (3rd century BC) uses the longer LXX chronology from the very beginning of that translation tradition. Josephus uses the LXX begetting ages. Luke includes Cainan. Jubilees includes Cainan in a Qumran manuscript. The shorter MT numbers have no independent witness before the late 1st century AD rabbinic standardization.