Another fundamental problem in the genetics of hypertension is the definition of the ancestral phenotype. Hypertension is a disease of modern civilisation and heavily depends on environmental and particularly dietary factors of modern society. For example, members of the Luo tribe had lower blood pressure in their traditional rural environment than in the urban environment of Nairobi where their urinary sodium concentration was higher and urinary potassium concentration was lower [12]. It has been hypothesised that in a sodium-deprived environment the default genotype is a sodium conserving one. Likewise, the renin–angiotensin–aldosterone system may have initially been adapted for sodium conservation but may play an important role in the pathogenesis of hypertension in modern societies with high dietary salt intake [13]. These considerations highlight that for genes associated with hypertension the disease allele does not necessarily have to be the minor (rare) allele but could be the major (for examples sodium conserving) allele as well, and that studies into genes associated with low blood pressure could be equally important for the genetics of hypertension.