Boozy chimps, Hanuman and the “drunken monkey” hypothesis

A new paper reports on chimpanzees in Guinea exhibiting long-term and recurrent ingestion of ethanol. The study was carried out over 17 years and found chimpanzees using leaves to drink fermented palm sap. Many consumed sufficient to produce “visible signs of inebriation”. Local humans also tap the sap of the raffia palm trees to make a palm wine.

The human trait of imbibing intentionally fermented drinks is at least as old as the oldest known archaeological records of ancient civilizations. Stone jugs for alcoholic drinks have been found which date back to at least 10,000 BCE . It is quite likely that the origin of alcoholic drinks predates the arrival of agriculture some 15,000 years ago. And that would suggest that the origin lies with the accidental (and fortuitous?) consumption of over-ripe and partially fermented fruits and berries leading eventually to an intentional fermentation. But that takes the origin back to the time before modern humans had even arrived on the scene and when their primate ancestors relied on fruits and berries for their diet.

Kimberly J Hockings, et al, Tools to tipple: ethanol ingestion by wild chimpanzees using leaf-sponges, Royal Society of Open Science

AbstractAfrican apes and humans share a genetic mutation that enables them to effectively metabolize ethanol. However, voluntary ethanol consumption in this evolutionary radiation is documented only in modern humans. Here, we report evidence of the long-term and recurrent ingestion of ethanol from the raffia palm (Raphia hookeri, Arecaceae) by wild chimpanzees (Pan troglodytes verus) at Bossou in Guinea, West Africa, from 1995 to 2012. Chimpanzees at Bossou ingest this alcoholic beverage, often in large quantities, despite an average presence of ethanol of 3.1% alcohol by volume (ABV) and up to 6.9% ABV. Local people tap raffia palms and the sap collects in plastic containers, and chimpanzees use elementary technology—a leafy tool—to obtain this fermenting sap. These data show that ethanol does not act as a deterrent to feeding in this community of wild apes, supporting the idea that the last common ancestor of living African apes and modern humans was not averse to ingesting foods containing ethanol.

The study provides support for the “drunken monkey” hypothesis which “proposes that human attraction to ethanol may derive from dependence of the primate ancestors of Homo sapiens on ripe and fermenting fruit as a dominant food source. Ethanol naturally occurs in ripe and overripe fruit when yeasts ferment sugars, and consequently early primates (and many other fruit-eating animals) have evolved a genetically based behavioral attraction to the molecule”.

In fact there were natural selection benefits in being “drunken monkeys”. The chimpanzee paper begins:

The ‘drunken monkey hypothesis’ states that natural selection favoured those primates with an attraction to ethanol (commonly referred to as alcohol) because it was associated with proximate benefits (e.g. acting as an appetite stimulant or a cue to finding fruit, or as an unavoidable consequence of a frugivorous diet, etc.), consequently increasing caloric gains.

Hanuman chasing the Sun — image Wikipedia

It is a short mental step from monkey-ancestors to ancient civilizations and mythology. The Indian monkey-god, Hanuman was supposed to be both celibate and teetotal. But his depiction as a “monkey” is probably a later invention. Ancient texts suggest that the young Hanuman was so enamoured of red fruit that he tried to eat the Sun, thinking it was just another ripe fruit. Quite possibly his red fruit were over-ripe, partially fermented and intoxicating. The resulting disfigurement to his jaw and face (burnt and swollen) is what may have given him his appearance. There is a hint that he was of an ancient people (species), half-human and half-monkey, which has become extinct. An ancient ancestor perhaps, and one addicted to intoxicating fruit. Clearly he was put off alcohol for ever. Interestingly, mythology and ancient ayurvedic medicine agree that alcohol in moderation is medicinal and good but taken in excess is a poison and bad. Of course in the Ramayana, all the good guys are vegetarians and teetotal while all the bad guys eat meat and consume an excess of alcohol. The Mahabharata is much more equivocal. Here even the good guys are allowed to drink.

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