Genetic study revives myth of drunken elephants

New research by a team of Canadian anthropologists suggests that a famously debunked story about drunk elephants may contain a kernel of truth after all. Researchers have studied a number of mammals for the presence of a genetic mutation linked to improved ethanol metabolism, finding that very few animals actually have the ability to rapidly process alcohol.

In 2005, a team of biologists from the University of Bristol claimed to debunk a common amusing anecdote. The oft-told story was that African elephants searched for fallen fruit from the malura tree. The naturally sweet fruit is known to ferment quickly when it drops to the ground, reaching around three percent ethanol concentration after just a few days.

Tales of drunken elephants storming villages were commonly shared for decades, until the Bristol team published a study concluding that it would be nearly impossible for large mammals to consume enough fermented fruit. to reach a state of intoxication. The 2005 study suggested that the anecdotal accounts were simply a case of anthropomorphism, with human characteristics projected onto the animals.

However, a new study suggests that previous research may fall victim to its own set of anthropomorphic biases, calculating intoxication based on the rates of ethanol metabolism unique to humans.

The new study focused on a gene called ADH7. This gene is known to produce an enzyme that metabolizes ethanol. While the gene itself is present in many mammals, the study identifies a mutation in the gene that improves the efficiency of ethanol metabolism by 40 times.

The mutation is thought to have happened around 10 million years ago, when we came down from the trees and encountered a lot more fermented fruit on the ground. This mutation was necessary in order to be able to eat more fruit without becoming intoxicated and vulnerable to predators.

Mammals sharing a common lineage all still have this mutated version of ADH7, including gorillas and chimpanzees. The mutation was also observed in a line of fruit bats, obviously evolving the need to be able to eat fermenting fruits without getting too drunk to fly. And, strangely enough, the mutation was found in koalas. The presence of the mutation in koalas is suggested to help the animals process certain toxins found in eucalyptus leaves.

The implication of the new study is that the anecdotal story of drunken elephants may not be so apocryphal after all. Mareike Janiak, a University of Calgary anthropologist working on the new research, suggests that the study is not designed to prove the drunken elephant story to be true, but rather serves to remind people that we must be careful when we extrapolate human metabolic functions to animals.

“If you can’t metabolize ethanol very quickly, you’re more likely to feel the effects or have a lower threshold for how much you can consume,” says Janiak. “We don’t prove the stories to be true, but we question the previous debunking. The anecdotes could be true.”

The new study was published in the journal Biology letters.

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