Did the Masoretic Text or the Septuagint change the patriarchal ages in Genesis?

The external evidence points toward the Masoretic Text reducing the numbers — not the Septuagint inflating them.

Here's why this matters. The two oldest witnesses to Genesis 5 and 11, the Hebrew Masoretic Text (MT) and the Greek Septuagint (LXX), disagree on the patriarchal begetting ages by exactly 100 years per patriarch — consistently, across six of the seven pre-flood figures and six of the eight post-flood figures. That kind of precision rules out accidental scribal error. Someone changed the numbers on purpose.

The question is direction: did the LXX add 100 years to each patriarch, or did the MT remove them?

Four independent witnesses all point the same direction. Demetrius the Chronographer was writing in the 3rd century BC — contemporary with the Septuagint translation itself — and he uses the longer begetting ages. His work predates any surviving MT manuscript by over a thousand years. Josephus, writing in AD 93, uses LXX-style numbers for the begetting ages even while following the MT's genealogical structure. Luke includes an extra patriarch, Cainan, between Arphaxad and Shelah (Luke 3:36) — Cainan appears in the LXX but not the MT. The book of Jubilees, attested at Qumran in 15 fragmentary manuscripts and dated to the 2nd century BC, includes Cainan with his own narrative.

The shorter MT numbers have no independent witness before the late 1st–2nd century AD, when rabbinic scholars standardized the Hebrew text. That's a striking gap: every early witness — Greek, Latin, Jewish historian, New Testament, Dead Sea Scrolls — runs long.

A possible reason for the reduction: the longer chronology was being used in messianic calculations by both Christians and competing Jewish groups. Reducing the begetting ages disrupted those calculations while leaving the total lifespans unchanged — a targeted, traceable change that affected chronology without touching biography.

Read the full study on the patriarchal chronology