New Evidence For The 'Drunken Monkey' Hypothesis

A new study into the behaviour of chimps lends support to the so called ‘drunken monkey’ hypothesis.

Wild chimpanzees in Uganda and Ivory Coast consume enough naturally fermenting fruit to ingest the equivalent of nearly two alcoholic drinks a day, according to the study.

Researchers measured ethanol levels in fallen fruit and found chimps selectively ate the ripest pieces, rich in sugar and alcohol. The findings lend weight to Robert Dudley’s theory that human attraction to alcohol has deep evolutionary roots that date back tens of millions of years.

Dudley's drunken monkey theory proposes that human attraction to alcohol 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 over-ripe fruit when yeasts ferment sugars, and consequently early primates (and many other fruit-eating animals) have evolved a genetically based behavioural attraction to the molecule.

This idea was originally proposed by Robert Dudley of the University of California at Berkeley, and was the subject of a symposium at the 2004 annual meeting of the Society for Integrative and Comparative Biology. Ten years later, his book The Drunken Monkey: Why We Drink and Abuse Alcohol was published, with Dudley suggesting that, whereas most addictive substances have a relatively short history of human use, attraction to and consumption of ethanol by various primates may go back tens of millions of years.

The odours of ripening fruit would help primates find scarce calories in tropical rain forests, given that ethanol is a relatively light molecule and is moved rapidly by winds through vegetation. This once-beneficial attraction to and consumption of ethanol at low concentrations may underlie modern human tendencies for the enjoyment of alcohol.