Humans may have turned drinking into something of an art form, but when it comes to animals that dispose of alcohol, Homo sapiens is no such outlier, researchers say.
A review of published evidence shows that alcohol occurs naturally in nearly every ecosystem on Earth, making it likely that most animals that feast on sugary fruits and nectar regularly imbibe the intoxicant.
Although many creatures have evolved to tolerate a drop and get little more than calories from their consumption, some species have learned to protect themselves with alcohol. Others, however, seem less able to cope with its consequences.
“We are moving away from this anthropocentric view that alcohol is only used by humans and that ethanol is actually quite abundant in the natural world,” said Anna Bowland, a researcher in the team at the University of Exeter.
After tracking down research papers on animals and alcohol, the scientists came up with a “diverse coterie” of species that embrace and adapt ethanol in their diet, which usually comes from fermented fruit, juice and nectar.
Ethanol became abundant on Earth about 100m years ago when flowering plants began to produce sugary fruits and nectar that yeast could ferment. The alcohol content is typically low, at around 1% to 2% alcohol by volume (ABV), but in overripe palm fruit the concentration can reach 10% ABV.
In one study, wild chimpanzees in southeastern Guinea were caught on camera relaxed to the alcoholic juice of raffia palms. Meanwhile, spider monkeys on Barro Colorado Island, Panama, are partial to ethanol-laden yellow mombine fruit, which appears to contain between 1% and 2.5% alcohol. “Evidence is growing that people do not drink alone,” the authors write Trends in Ecology and Evolution.
Whether consumption leads to intoxication is another question. Stories of drunken animals abound, from elephants and baboons drunk on marula fruit in Botswana, to a moose found with its head stuck in a tree in Sweden after munching on fermented apples. But in none of these cases was at least alcohol measured in the animals or the fruit.
Many animals appear to have impressive alcohol tolerance. Despite the pin-tailed tree-knife’s “enormous ethanol consumption”, the scientists found no evidence that the animals had become intoxicated, but conceded that it was “unclear how a drunken mouse would behave”.
Animals that regularly eat fermented foods tend to metabolize alcohol quickly, sparing them its worst effects. But some creatures encounter ethanol less frequently and may suffer the effects. Tests on cedar waxwings, which were killed by crashing into fences and other structures, found that they flying under the influence after feasting on the overripe berries of the Brazilian pepper tree. “Inebriation is not beneficial in an environment where you are fighting to survive,” Bowland said.
Perhaps the most striking effects of alcohol are seen in insects. Male fruit flies turn to alcohol when they are rejected as a mate, while females become of a closely related species less picky about their partners and have sex with more men after drinking. Fruit flies lay their eggs in ethanol-rich foods and protect them from parasites.
Earlier this month, researchers led by Eran Levin at Tel Aviv University found that oriental hornets may be the only animals capable of consuming an unlimited amount of alcohol without adverse effects. “They can ingest up to 80% ethanol solution without any negative effects on their mortality or behavior,” said Dr Sophia Bouchebti, an author of the study.
“Apart from the fruit fly, aye aye and slow loris, it is unclear whether animals prefer ethanol-containing foods,” said Matthew Carrigan at the College of Central Florida, who worked with Bowland on the review. “One of our next steps is to test whether animals in the wild prefer ethanol-containing food or only eat it when ethanol levels are too low to detect or unfermented fruit is hard to find.”
