Arginine vasopressin (AVP) is a neurohypophyseal hormone synthesized in the hypothalamus and released by the posterior pituitary that primarily functions in maintaining water homeostasis and vascular tone 1. AVP binds to specific receptors (V2 receptors in kidneys, V1 receptors elsewhere) to regulate aquaporin-2 water channel expression and promote water reabsorption in renal collecting ducts, thereby concentrating urine and conserving body fluids 2. Beyond osmoregulation, AVP plays critical roles in stress response modulation and social behavior regulation, with evidence suggesting reduced central AVP activity may facilitate domestication through decreased aggression and stress response 3. AVP gene mutations cause autosomal dominant familial central diabetes insipidus (CDI), characterized by progressive destruction of AVP-secreting neurons and polyuria exceeding 50 mL/kg/24 hours 45. Central DI results from inadequate AVP secretion due to hypothalamic or pituitary dysfunction, distinguishable from nephrogenic DI (kidney resistance to AVP) and primary polydipsia through water deprivation testing and copeptin measurement 2. Treatment with synthetic AVP analogues (desmopressin) effectively replaces deficient hormone, though hyponatremia remains a clinical concern 4. Population-level genetic variation in AVP and vasopressin receptor genes shows positive selection signatures, suggesting adaptive significance for emotional and social responses across human populations 6.