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The 'drunken monkey' hypothesis

Alcohol Use Disorder (AUD) is one of the most common addictive substance abuses. It's estimated that in the US alone, there more than 3 million early deaths each year as a result.( ref.)

Leading to the question - why do humans have such a preference for alcohol?

In 2000, a study published in The Quarterly Review of Biology pointed out that distant ancestors of humans may well have been adapted to alcohol consumption through eating fermented fruit (which commonly has an alcohol content of 5% or so).

Because human alcoholism (and drug addictions generally) are apparently unique in the animal kingdom, our perception and treatment of these diseases have been largely decoupled from the biological context within which our nutritional and sensory physiology evolved. However, an evolutionary perspective places intraspecific and interspecific variation in preference for ethanol, together with hormetic effects of this substance, within a broader and perhaps methodologically more tractable framework."

Source : Evolutionary Origins of Human Alcoholism in Primate Frugivory, [ paywalled ] The Quarterly Review of Biology, Volume 75, Number 1,

In 2014, another study attempted to trace the origins of the digestive alcohol dehydrogenases enzyme ADH4 (which enables the metabolism of alcohol) from our primate ancestors - with the finding that it goes back at least 10 million years - long before modern-day humans existed. See : Hominids adapted to metabolize ethanol long before human-directed fermentation PNAS Evolution, 112 (2) 458-463

In the same year professor Dudley of the University of California, Berkeley, published the 'Drunken Monkey hypothesis' - in a book which described to a wider audience possible links between the fruit-eating behavior of tropical arboreal primates and the evolution of sensory skills required to find ripe and fermented fruits that contain sugar and low levels of alcohol. Ref. The Drunken Monkey: Why We Drink and Abuse Alcohol., Berkeley: University of California Press. 154 pp. (Note: the book's web-page has reference links to many other academic studies on the subject.)

It's worth noting that there are many well-documented reports about other mammalian species (and some birds) becoming comprehensively drunk after eating fermented fruit. But, in contrast to humans, they tend not to make a habit of it.

Also see : Alcohol intoxicationplugin-autotooltip__plain plugin-autotooltip_bigAlcohol intoxication

"Despite the fact that alcohol has been used and misused for hundreds of years, the mechanism of action of this simple molecule remains the subject of study. Alcohol use results in diverse behavioral effects, including intoxication, cognitive impairment, motor incoordination, tolerance and dependence, and these effects are likely due to its actions on multiple brain proteins.

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