MILTON, K; Univ. of California, Berkeley: Primate Frugivory and Ethanol Ingestion

The evolution of higher primates is intimately bound up with the exploitation of ripe, fleshy fruits. Due to large body size and greater demands for energy and nutrients than monkeys, great apes in particular may at times be forced to feed on fruits well past the climacteric — the point at which ethanol concentrations can become relatively high. In anthropoids, detoxification of ethanol activates energetically wasteful metabolic pathways, lowers nutrient absorption and can lead to inefficient energy utilization. Excess energy from ethanol cannot be stored as fat. In females, ingested ethanol may harm the developing fetus. For these reasons, it would be predicted that wild primates, particularly females, would try to minimize their intake of ethanol insofar as possible and would seek actively to avoid rather than ingest overly-ripe fruits�a prediction some field observations appear to support. Many fossil and extant apes exhibit pronounced intraspecific sexual dimorphism in body size. Larger males would require absolutely more fruit per day than females and for this reason might habitually have ingested larger quantities of over-ripe fruits than females. This could have selected for a more efficient ethanol detoxification system in males. Because of potential fetal damage, females should be more sensitive to levels of ingested ethanol. Modern human females exhibit a lower level of alcohol metabolizing enzyme ADH in the stomach than males and also are significantly more prone to alcohol-related diseases. To date, no satisfactory explanation has been proposed for this sex-based difference. It is possible that this difference in modern humans may represent a “carry-over” effect, acquired by pre-human ancestors during their long evolutionary history as sexually dimorphic, fruit-eating hominoids.