Why mammals like elephants and armadillos might get drunk easily

An elephant, a narwhal and a guinea pig walk into a bar. From there, things could get ugly.

All three might get drunk easily, according to a new survey of a gene involved in metabolizing alcohol. They’re among the creatures affected by 10 independent breakdowns of the ADH7 gene during the history of mammal evolution. Inheriting that dysfunctional gene might make it harder for their bodies to break down ethanol, says molecular anthropologist Mareike Janiak of the University of Calgary in Canada.

She and colleagues didn’t look at all the genes needed to metabolize ethanol, but the failure of this important one might allow ethanol to build up more easily in these animals’ bloodstreams, Janiak and colleagues report April 29 in Biology Letters.

The carnivorous cetaceans, grain- or leaf-eating guinea pigs and most other animals that the study identified as potentially easy drunks probably don’t binge on sugary fruit and nectar that brews ethanol. Elephants, however, will feast on fruit, and the new study reopens a long-running debate over whether elephants truly get tipsy gorging on marula fruit, a relative of mangoes.

Descriptions of elephants behaving oddly after binging on overripe fruit go back at least to 1875, Janiak says. Later, a taste test offering the animals troughs of water spiked with ethanol found that elephants willingly drank. Afterward, they swayed more when moving and seemed more aggressive, observers reported.

Yet in 2006, physiologist Steve Morris of the University of Bristol in England and colleagues attacked the notion of elephant inebriation as “a myth.” Among their arguments was a calculation that even if African elephants really were feasting on fallen, fermenting marula fruit, the animals could not physically eat the huge amount necessary at one time to get a buzz (SN: 6/13/17). However, that calculation extrapolated from human physiology. The new insight that elephants’ ADH7 gene doesn’t work might mean they have a lower tolerance for the tipple.

It wasn’t elephants, though, but tree shrews that inspired the new work (SN: 7/28/08). They look like “cute squirrels with pointed noses,” says senior author Amanda Melin, a biological anthropologist also at Calgary, and they have a prodigious tolerance for alcohol. Concentrations of ethanol that would make a human sloppy apparently don’t phase the little animals. She, Janiak and colleagues decided to survey all of the mammal genetic information that they could find to indirectly assess the variety of responses to alcohol. “We were on a patio drinking beer when we first sketched out the paper,” Janiak remembers.

Looking at genetic information available on 79 mammal species, researchers found that ADH7 has lost its function in 10 separate spots on the mammal family tree. These ethanol-susceptible twigs sprout quite different animals: elephants, armadillos, rhinos, degus, beavers and cattle among them.

In contrast, humans and nonhuman African primates have the reverse situation, a mutation that renders their ADH7 some 40 times more efficient at dismantling ethanol than a typical mammalian version. Aye-ayes, with diets rich in fruit and nectar, have independently evolved the same trick (SN: 10/22/19). What gives tree shrews their drinking superpower, however, remains a mystery since they don’t have the same superefficient gene.

Finding the gene dysfunction in the African elephant, however, raises questions about the old inebriation arguments. A slower capacity for clearing ethanol from the body could mean that the smallish amount that an elephant gets from eating its full of fermented fruit might be enough to change their behavior after all, Melin says.

Behavioral ecologist Phyllis Lee has been watching elephants in Kenya’s Amboseli National Park since 1982 and is now director of science for Amboseli Trust for Elephants. “In my youth, we tried to brew a form of maize beer (we were desperate), and the elephants loved to drink it,” she says. She does not take sides in the myth debate, although she muses about the “huge liver” of elephants, which would have at least some detoxifying power.

“I never saw one that was tipsy,” Lee says, although that home brew “didn’t do much for us puny humans either.”