Does a parasite have a better chance of survival if an Inuit or a Mayan spits on it?

Abstract

An earlier puzzling observation [Shields and Mann, J Craiofac Genet Dev Biol, 16:126-136, 1996] that the prevalence of a polymorphic male predominate, major salivary gland-associated, static lesion of the mandible increased exponentially from the Arctic to the Tropics was explained by both positive and negative selection (balancing) on major salivary gland endocrine and exocrine factors. Additional prevalence rates presented here identified three high prevalence high-Temperate zone cultures that were unusually exposed to alimentary parasites. A correlation between macroparasite exposure and the mandibular lesion helped refine the potential selective forces that fashioned major salivary gland size variation. The data suggests that positive selection occurred for androgen-induced enlargement of the suite of major salivary glands and consequently increased quantities of factors. Increased quantities of salivary gland biologically active factors enhance innate protection against infestation of macroparasites per se, especially gut parasites. The data further suggests that negative selection against enlarged salivary glands occurred as protection against electrolyte imbalances in electrolyte stressed environments and in females.