Contemporary patterns of alcohol consumption, in turn, may derive from these ancestral associations between ethanol and nutritional reward. Psychoactive and hedonic effects of ethanol may similarly result in increased consumption rates and caloric gain. Human ancestors may also have preferentially selected ethanol-laden fruit for consumption (via short-range olfaction and also via gustation), given that its presence necessarily indicates co-occurrence of simple sugar precursors. Ethanol is a by-product of fermentative yeasts within fruit pulp that metabolize sugar in the ripening process and that may serve as a long-distance olfactory cue to animal frugivores, including many primates. The ‘drunken monkey’ hypothesis posits that the proclivity of humans to consume alcohol stems from a deep-rooted affinity of frugivorous primates for naturally occurring ethanol within ripe fruit.

In aggregate, these data indicate natural exposure to fruit-associated ethanol in a wild primate species.

Urine samples from foraging spider monkeys were also evaluated for the ethanol metabolites ethyl glucuronide and ethyl sulfate five of six samples tested positive for both compounds. Of collected fruits that were partially consumed and then dropped by foraging monkeys, pulp-ethanol content was typically in the range of 1–2% the percentage of pulp for consumed fruits was not significantly correlated with the ethanol concentration of the pulp remaining within each fruit. Here, we present data on ethanol concentrations within fruits of Spondias mombin (Anacardiaceae) that are eaten by black-handed spider monkeys ( Ateles geoffroyi) on Barro Colorado Island, Panama. As a consequence, frugivorous animals may chronically consume ethanol as part of their routine diet, although direct measurements of such exposure are lacking. Ethanol within ripe and over-ripe fruit is produced naturally through the metabolic activity of fermentative yeasts.

Spider mokey