Hypertension is a polygenic disease of world-wide concern. So far, no polygenic disease has been solved at the genetic level. Ethnic differences in the prevalence of hypertension may suggest candidate genes worthy of study. A strong genetic predisposition to hypertension and target organ damage appears to correlate with African ancestry, referred to as "the African gene." Sub-Saharan Africans have endured the selective pressure of extreme heat for thousands of generations. Polymorphisms in the renin-angiotensin system, such as the recently described insertion/deletion polymorphism in the angiotensin I converting enzyme (ACE) gene, may predispose to hypertension and related disorders because of an advantage they confer in thermoregulation.