The Drunken Monkey: Is Alcohol Consumption by Modern Humans an Evolutionary Hangover?

Ethanol derives from the fermentation of simple sugars, and fermentative yeasts are ubiquitous within terrestrial ecosystems. Animals that routinely consume sugar-rich fruits and nectar thus outinely ingest low-level ethanol, although typical concentrations and consumed volumes are not well known. The sensory capacity to detect and follow ethanol plumes enables localization of ripe fruits over long distances, as occurs in fruit flies. Positive psychoactive responses to ethanol among vertebrate fruit-eaters (and modern humans) can also act to increase net caloric gain during feeding via the aperitif effect. Moreover, paleogenetic reconstruction of one of the enzymes involved in ethanol metabolism (ADH) suggests sustained exposure of human ancestors over the last 12 million years to dietary ethanol. Patterns of alcohol use by modern humans may thus reflect ancestral sensory biases associating ethanol consumption with nutritional reward (i.e., the "drunken monkey" hypothesis). I will also present recent measurements of ethanol concentrations within wild fruit and nectar, together with comparative behavioral, physiological and genomic data among fruit- and nectar-eaters that corroborate this hypothesis, and will discuss implications for understanding the origins of alcoholism in modern humans.