Dietary ethanol ingestion by free-ranging spider monkeys (Ateles geoffroyi).

Christina J Campbell,Victoria Weaver,Aleksey Maro,Robert Dudley

doi:10.1098/rsos.211729

Abstract

Ethanol within ripe and over-ripe fruit is produced naturally through the metabolic activity of fermentative yeasts. As a consequence, frugivorous animals may chronically consume ethanol as part of their routine diet, although direct measurements of such exposure are lacking. 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. 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. 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. In aggregate, these data indicate natural exposure to fruit-associated ethanol in a wild primate species.

Highlights

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 [1,2]
Fruits of S. mombin that were partially consumed by spider monkeys contained measurable ethanol within the remaining pulp
The ethanol content of pulp obtained from fully intact and ripe fruits collected on the forest floor in the absence of foraging spider monkeys was near 2%

Summary

Introduction

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 [1,2]. 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. Human ancestors may have preferentially selected ethanol-laden fruit for consumption (via short-range olfaction and via gustation), given that its presence necessarily indicates co-occurrence of simple sugar precursors [3,4]. Psychoactive and hedonic effects of ethanol may result in increased consumption rates and caloric gain. Contemporary patterns of alcohol consumption, in turn, royalsocietypublishing.org/journal/rsos R.

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