Organs without common ancestry: testable criteria

Abstract. Whether the gut mucosa–microbiota complex is an organ is debated as though the criteria for organ status were settled. They are not: no authority publishes organ criteria, and textbook definitions are hedged statements that papers convert into necessary conditions. We make the de facto criteria explicit (C1–C5) and show by scoring accepted organs that two conditions used to exclude the microbiota fail: common embryological origin is falsified by the adrenal gland, pituitary, placenta, skin and immune system, and anatomical distinctness by blood and the immune system. We propose four replacement criteria — bounded compartment, host-maintained configuration, coordinated function, identifiable causal consequences — that accept self-falsification. The complex satisfies all four and yields testable predictions for intervention design and postmortem microbiology. Type. Conceptual framework paper / hypothesis. No new data are reported; all cited datasets are public. Version. v0.2 — supersedes v0.1.