Monkeys routinely consume fruit containing alcohol, shedding light on
our own taste for booze
Study supports 'drunken monkey' hypothesis: humans inherited love of
alcohol from primate ancestors

Date:
April 1, 2022
Source:
University of California - Berkeley
Summary:
Scientists analyzed the ethanol content of fruit eaten by spider
monkeys in Panama, and found that the fruit regularly contained
alcohol: between 1% and 2%. The researchers also collected
urine samples, most of which contained secondary metabolites of
ethanol. The results provide further evidence that our primate
ancestors preferentially sought out fermented, alcohol-containing
fruit likely for its greater nutritional value, and that humans
may have inherited this proclivity for ethanol.



FULL STORY ==========================================================================
For 25 years, UC Berkeley biologist Robert Dudley has been intrigued
by humans' love of alcohol. In 2014, he wrote a book proposing that
our attraction to booze arose millions of years ago, when our ape and
monkey ancestors discovered that the scent of alcohol led them to ripe, fermenting and nutritious fruit.


==========================================================================
A new study now supports this idea, which Dudley calls the "drunken
monkey" hypothesis.

The study was led by primatologist Christina Campbell of California State University, Northridge (CSUN), and her graduate student Victoria Weaver,
who collected fruit eaten and discarded by black-handed spider monkeys
(Ateles geoffroyi) in Panama. They found that the alcohol concentration
in the fruit was typically between 1% and 2% by volume, a by-product of
natural fermentation by yeasts that eat sugar in ripening fruit.

Moreover, the researchers collected urine from these free-ranging monkeys
and found that the urine contained secondary metabolites of alcohol. This result shows that the animals were actually utilizing the alcohol for
energy -- it wasn't just passing through their bodies.

"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, a CUSN professor of anthropology
who obtained her Ph.D. in anthropology from Berkeley in 2000. "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." Dudley laid out evidence for his idea eight years ago in the
book, The Drunken Monkey: Why We Drink and Abuse Alcohol. Measurements
showed that some fruits known to be eaten by primates have a naturally
high alcohol content of up to 7%. 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 newly reported study, the CSUN researchers teamed up with
Dudley and UC Berkeley graduate student Aleksey Maro to analyze the
alcohol content in the fruits. Maro is conducting a parallel study of
the alcohol content in the fruit-based diet of chimpanzees in Uganda
and the Ivory Coast.

"It (the study) is a direct test of the drunken monkey hypothesis,"
said Dudley, UC Berkeley professor of integrative biology. "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, which appeared this month in the journal Royal Society Open
Science, was conducted at a field site, Barro Colorado Island in Panama,
where Dudley has often conducted research and where he first began
thinking about the role of ethanol in animal diets and how that might
play into our enjoyment and abuse of alcohol.

The researchers found that the fruit that spider monkeys sniffed and took
a bite out of routinely had alcohol concentrations of between 1% and 2%,
about half the concentration of low-alcohol brews The ripe fruits they 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.



==========================================================================
"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 said that he doubts that the monkeys feel the inebriating effects
of alcohol that humans appreciate.

"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 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, Campbell said.

"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." Today, the availability of alcohol
in liquid form, without the gut-filling pulp of fermenting fruit, means
it's easy to overindulge. 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.

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


========================================================================== Story Source: Materials provided by
University_of_California_-_Berkeley. Original written by Robert
Sanders. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* Black-handed_spider_monkey ========================================================================== Journal Reference:
1. Christina J. Campbell, Aleksey Maro, Victoria Weaver, Robert Dudley.

Dietary ethanol ingestion by free-ranging spider monkeys (Ateles
geoffroyi ). Royal Society Open Science, 2022; 9 (3) DOI: 10.1098/
rsos.211729 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220401141345.htm

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