A bloodline. A family curse. The bite that spreads.

LERV integrated in the lineage ancestral to sapiens and neanderthalensis roughly eight hundred thousand years before present. Envelope homology points at a canid-adapted retroviral ancestor — the ecological setting of H. heidelbergensis and proto-wolf: shared carcasses, competition, eventual mutualism, the exact context in which cross-species retroviral jumps occur. Approximately eight percent of the human genome is already retroviral fossil. LERV is the insertion that still fires.

Functionally significant integrations concentrate on chromosome 6, adjacent to the MHC, which is how the immune system is taught to tolerate LERV proteins during the shift, and on chromosome 17 and a third cluster that carry the structural and regulatory genes of the hydraulic engine. Copy-number variation between individuals is the primary source of phenotypic threshold. Most carriers never shift. Methylation keeps the cassette locked. The folklore of the bloodline is population genetics. The folklore of the bite is a separate, incomplete, and costly transmission route.