Humans may have developed our taste for alcohol from primates

By Jim Leffman via SWNS

Humans may have developed a taste for alcohol from our primates that ate fermented fruits, containing alcohol, suggests a new study.

The 'drunken monkey' theory is based on modern-day apes who seek out over-ripe fermented fruit for the alcohol.

American researchers believed that the smell of alcohol led our ancestors to ripe and nutritious fruit millions of years ago.

Although just a theory when it was first proposed by University of California Berkley biologist Professor Robert Dudley in 2014, new evidence amongst modern monkeys seems to support it.

The latest study by primatologist Professor Christina Campbell of California State University, Northridge (CSUN), looked at fruit collected from black-handed spider monkeys in Panama.

Along with her team, they found that the alcohol content in the ripened fruit discarded was typically between one percent and two percent by volume, about half the strength of beer.

The researchers collected urine from these free-ranging monkeys and found that it contained secondary metabolites of alcohol.

This result shows that the animals were actually using the alcohol for energy — it wasn't just passing through their bodies.

Prof Campbell said: "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.

"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 fruit-eating primates for naturally-occurring ethanol within ripe fruit.”

In his book outlining his 'drunken monkey' theory, Prof Dudley said that some fruits known to be eaten by primates have a naturally high alcohol content of up to 7%, half that of wine.

But at the time, he did not have data showing that monkeys or apes preferentially sought out and ate fermented fruits, or that they digested the alcohol in the fruit.

For the new study, the CSUN researchers teamed up with Dudley to analyze the alcohol content in the fruits.

They are currently conducting a parallel study of the alcohol content in the fruit-based diet of chimpanzees in Uganda and the Ivory Coast.

Prof Dudley said: ""The new study is a direct test of the drunken monkey hypothesis.

"Part one, there is ethanol in the food they're eating, and they're eating a lot of fruit.

"Then, part two, they're actually metabolizing alcohol. Secondary metabolites, ethyl glucuronide and ethyl sulfate are coming out in the urine.

"What we don't know is how much of it they're eating and what the effects are behaviorally and physiologically. But it's confirmatory."

The study, published in the journal Royal Society Open Science, was conducted at a field site, Barro Colorado Island in Panama.

The ripe fruits the monkeys collected were from the jobo tree, Spondias mombin, and were a major component of the spider monkey diet.

But the fruit also has been used for millennia by Indigenous human populations throughout Central and South America to make chicha, a fermented alcoholic beverage.

The researchers also collected urine from six spider monkeys. Five of the samples contained secondary metabolites of ethanol.

Prof Campbell said: “The monkeys were likely eating the fruit with ethanol for the calories.

“They would get more calories from fermented fruit than they would from unfermented fruit. The higher calories mean more energy.”

However, Prof Dudley said that he doubts that the monkeys get drunk in the same way humans do.

He said: "They're probably not getting drunk, because their guts are filling before they reach inebriating levels.

"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 predigesting the fruit. You can't rule that out."

The need for the monkeys’ high caloric intake may similarly have influenced human ancestors’ decisions when choosing which fruit to eat, Prof Campbell said.

“Human ancestors may also have preferentially selected ethanol-laden fruit for consumption, given that it has more calories."

“Psychoactive and hedonic effects of ethanol may similarly result in increased consumption rates and caloric gain.”

The idea that humans' natural affinity for alcohol is inherited from our primate ancestors could help society deal with the adverse consequences of alcohol abuse.

Prof Campbell added: “Excessive consumption of alcohol, as with diabetes and obesity, can then be viewed conceptually as a disease of nutritional excess."