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Study on monkeys sheds light on our love of alcohol

  • August 9, 2022
  • 3 min read
Study on monkeys sheds light on our love of alcohol

Primatologists at California State University have supported the “drunken monkey” hypothesis. This is the belief that our love of alcohol arose millions of years ago from our monkey and ape ancestors, who discovered that the scent of alcohol led them to ripe, fermenting, and nutritious fruits. 

This study, led by primatologist Christina Campbell of California State University, Northridge (CSUN), and her graduate student Victoria Weaver, involved collecting fruit eaten and discarded by black handed spider monkeys in Panama. They found that the monkeys were utilising the alcohol for energy.

“For the first time, we have been able to show, without a shadow of a doubt, that wild primates, with no human interference, consume fruit-containing ethanol,” said Campbell. “This is just one study, and more need to be done, but it looks like there may be some truth to that ‘drunken monkey’ hypothesis — that the proclivity of humans to consume alcohol stems from a deep-rooted affinity of frugivorous (fruit-eating) primates for naturally-occurring ethanol within ripe fruit.”

The evidence was laid out eight years ago by UC Berkeley professor of integrative biology, Robert Dudley in his book, The Drunken Monkey: Why We Drink and Abuse Alcohol. Measurements found that some fruits eaten by primates had a naturally high alcohol content, as much as 7%. However, there was no evidence at the time that the animals sought out fermented fruits or that they digested the alcohol in them. 

This new study, published in the journal Royal Society Open Science, was conducted in Panama’s Barro Colorado Island. In addition to analysing the fruits that the monkeys were eating, they collected urine samples. 

“The monkeys were likely eating the fruit with ethanol for the calories,” Campbell said. “They would get more calories from fermented fruit than they would from unfermented fruit. The higher calories mean more energy.”

Dudley doubts that they are seeking alcohol for the same reason as us.

“They’re probably not getting drunk, because their guts are filling before they reach inebriating levels,” he said. “But it is providing some physiological benefit. Maybe, also, there’s an anti-microbial benefit within the food that they’re consuming, or the activity of the yeast and the microbes may be pre-digesting the fruit. You can’t rule that out.”

This need for high caloric intake, Campbell said, may have influenced our ancestors’ decisions on which fruit to eat. 

“Human ancestors may also have preferentially selected ethanol-laden fruit for consumption, given that it has more calories,” she said. “Psychoactive and hedonic effects of ethanol may similarly result in increased consumption rates and caloric gain. Excessive consumption of alcohol, as with diabetes and obesity, can then be viewed conceptually as a disease of nutritional excess.”

Today, we enjoy alcohol in liquid form and without the ‘gut-filling pulp’ of fermenting fruits. This makes it easy to overindulge. Learning more about our primate relatives’ love of alcohol can help us find solutions to the effects that alcohol has on our own society.

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