The relation between salt intake and hypertension has long been controversial. Available evidence provides conflicting results. However, biological and evolutionary insights into the structure and principle function of the kidney and the blood pressure sustaining machinery, with the extracellular fluid volume and the renin-angiotensin system acting as a central player, clearly indicate that salt has been a precious commodity in the terrestrial animal kingdom and that essential hypertension may be a consequence of the kidney's maladaptation to excess salt intake, which is specific to recent human civilization. This review provides a hypothesis to explain how and why hypertension develops and attempts to define the roles of genetic, non-genetic, and environmental factors in its pathogenesis.