THE BIOANTHROPOLOGICAL IMPACT OF CHRONIC EXPOSURE TO SUBLETHAL CYANOGENS FROM CASSAVA IN AFRICA

The regular ingestion of foods derived from cassava (Manihot esculenta Crantz) frequently exposes human consumers to sublethal levels of residual cyanogenic glucosides and their metabolic by-products. It is hypothesized that chronic exposure to low doses of these plant secondary compounds initiate and sustain an assortment of physiological and behavioral modifications in consumers, some of which may be of clinical and even bioevolutionary importance. In much of humid tropical Africa, cassava is widely eaten as a major carbohydrate staple and as a green leafy vegetable. In each dietary form, it is a potential biological source of sublethal cyanogens. Research in Liberia and elsewhere in Africa's rain forests and wet savannas suggests that a diet containing cassava may influence the biological fitness and distribution of certain hemoglobin genes, alter basic metabolic processes (e.g., gluconeogenesis, enzyme function, and thyroid hormone activity), stimulate the immune system, compromise central nervous system integrity, and decelerate the usual patterns of infant growth and development. The results of retrospective studies among humans have been evaluated and confirmed in swine-based experimental models. From these data, it is theorized that the high degree of phenotypic and genotypic variability observed among Africans residing in the humid tropics may reflect, in a large measure, the potentially dramatic influence of chronic dietary cassava use and exposures to cyanogenic glucosides and residual cyanogens on human metabolic biology, on disease susceptibility, and on the cadence and direction of human microevolution.