The drunken monkey: evolutionary origins of attraction to alcohol in primate frugivory

Ethanol derives from the fermentation of simple sugars, and fermentative yeasts are common within terrestrial ecosystems. Animals that routinely consume sugar-rich fruits and nectars thus chronically ingest low-level ethanol. The capacity to detect and follow ethanol plumes enables localization of ripe fruits and fermented nectars over long distances (as occurs in fruit flies); psychoactive responses to ethanol among vertebrate frugivores may increase net caloric gain during feeding via the aperitif effect.  Paleogenetic reconstruction of enzymes involved in ethanol metabolism suggests sustained exposure of hominids (including the genus Homo) over the last 12 million years to dietary ethanol.  Alcohol use by modern humans may thus derive from ancestral sensory biases associating ethanol consumption with nutritional reward (i.e., the "drunken monkey" hypothesis).  Detailed measurements of ethanol concentrations within fruit and nectar, together with behavioral, physiological and genomic comparisons among frugivores and nectarivores, are now necessary to further test this hypothesis.