"There are travellers' tales from about 1839 reporting Zulu accounts that 'elephants gently warm their brains with fermented fruits,'" Morris said. But there is nothing in the biology of either the African elephant or the marula fruit to support the stories, he contends. "Elephants display many behavioural characteristics viewed as positive traits in humans, often causing us to identify with them in anthropomorphic ways," write Steve Morris, David Humphreys, and Dan Reynolds in a forthcoming paper in Physiological and Biochemical Zoology. "The tipsy pachyderm is a view bolstered perhaps by a mutual desire for the fruits of the marula tree. People just want to believe in drunken elephants”.
The marula tree, a member of the same family as the mango, grows widely in Africa. Its sweet, yellow fruit is used for making jam, wine, beer, and a liqueur called Amarula. But the first flaw in the drunken-elephant theory is that it is unlikely that an elephant would eat the fruit if it were rotten. Elephants eat the fruit right off the tree, and will sometimes push over trees to get the fruit off the tree, even when rotten fruit is on the ground.
If fermented fruit on the ground is out of the question, so too is the notion that the fruit could ferment in the stomach of elephants, the study authors say. Believers of the drunken-elephant lore have often supported this theory of internal fermentation, but food takes between 12 and 46 hours to pass through an elephant's digestive system, which is not enough time for the fruit to ferment. Moreover, sugars within the diet are turned into fat before they can ferment into alcohol.
People just want to believe in drunken elephants
It is conceivable, the authors concede, that some small amount of ethanol could be produced in an elephant's digestive system, if its diet were rich enough in both yeast, which is necessary for fermentation, and fruit. Even in the unlikely event that these things happened, it's still highly improbable that the food would produce enough alcohol to make an elephant drunk. Through calculations of body weight, elephant digestion rates, and other factors, the study authors conclude that it would take about a half gallon (1.9 litres) of ethanol to make an elephant tipsy.
Assuming that fermenting marula fruit has an alcohol content of 7 percent, it would require 7.1 gallons (27 litres) of marula juice to come up with that half-gallon of alcohol, the scientists say. Producing a litre of marula wine requires 200 fruits. So an elephant would have to ingest more than 1,400 well-fermented fruits to even start to get drunk. Even then the elephant would have to ingest the alcohol all at once, the authors note. Otherwise its effects would wear off as quickly as the alcohol was metabolised.
It may make for a good story and a durable myth, but the science suggests you're not likely to see a drunken elephant sitting under a marula tree.