Surviving Bloodline Theory
That a Nephilim-descended lineage continued after the Flood and persists, unrecognised, in ordinary human populations today.
The theory
Nephilim descent passed through a Flood survivor or a post-Flood incursion, thinned across millennia into populations indistinguishable from anyone else — carried, in stronger versions, as a hidden trait or predisposition rather than visible stature.
What the text supports
Genesis 6:4's 'and also afterward' and the Numbers 13 report are the only textual footholds. Both are contested, and neither describes a continuing lineage into later history.
What would be required
A traceable line, a marker, or a source that names one. Currently none exists. Any 'thinned to invisibility' version is unfalsifiable by design — which is why it survives, not evidence that it is true.
Status
SPECULATIVE. Popular in modern books and online media; no textual, historical or genetic support.