Research identifies ‘alcoholism’ in monkeys

While analyzing the diet of black-handed spider monkeys (Ateles geoffroyi) in Panama, researchers found that the palm fruits that these animals regularly eat contain small doses of ethanol.

Urine samples from two of the spider monkeys also revealed specific metabolites of ethanol, suggesting that the alcohol doesn’t just pass through their bodies, but is absorbed and utilized in some way. of another.

“For the first time, we were able to show beyond a shadow of a doubt that wild primates, without human intervention, consume fruits containing ethanol,” said primatologist Christina Campbell of California State University, author research published in Royal Society Open Science. “It’s just a study, and there’s still a lot to do, but it looks like there might be some truth to that ‘drunken monkey’ hypothesis. »

The drunk monkey hypothesis was first put forward by UC Berkeley biologist Robert Dudley in 2000. He claims that the strong attraction that monkeys have for the smell and taste of ethanol is an evolutionary advantage that allows them to hunt ripe fruits, devouring them first. other animals can reach them.

The appetite for alcohol identified in our ancestors is no longer beneficial in humans

This same need for ethanol exists in our own species, but without exploiting the nutritional benefits of the whole fruit. Instead, humans learned to distill elements, and the “once advantageous appetite for alcohol” seen in our primate ancestors has now become a danger to our well-being.

It’s an interesting idea, but so far the evidence for this hypothesis has been limited and mostly anecdotal. Wild chimpanzees (pan troglodytes), for example, have been captured eating fermented palm sap, and in this sap have subsequently been found to have ethanol concentrations of almost 7%. However, it is not known whether the ethanol itself attracts chimpanzees to the fruit.

The survey conducted in Panama is the first to directly measure the consumption of fruits with ethyl content by primates. Captive spider monkeys have previously shown sensitivity to the smells of ripe fruits that contain ethanol, but this is the first study to show preferential consumption of these fruits in the wild.

According to research, spider monkeys not only eat lots of ethanol-containing fruits, but they also seem to metabolize fermented sugars. “The monkeys were probably consuming the calories from the fruit with ethanol,” says Campbell. “They would get more calories from fermented fruit than unfermented fruit. The more calories, the more energy.

A similar propensity may also exist in humans. In fact, the fruits eaten by spider monkeys are the same fruits used by indigenous human populations in Central and South America to make chicha, which is a fermented alcoholic drink.

When yeast feeds on sugar, it produces alcohol, presumably to fight off other competitors. The volatile compound then floats through the air, attracting animals like us to the juicy snack. The more fermented fruit we eat, the more energy we get and perhaps the more “drunk” we get.

In the case of the spider monkeys, however, Dudley suspects there is little drunkenness. The partially consumed fruits that the researchers tested contained only one or two percent ethanol. “They probably don’t get drunk, because their guts fill up before they get to the level of drunkenness,” Dudley says.

“But it provides physiological benefits. Also maybe there is an antimicrobial benefit in the food they eat, or yeast and microbial activity may pre-digest the fruit.

Monkeys and humans share a gene that makes the ethanol enzyme work

If there is an evolutionary benefit to alcohol, passed down over tens of millions of years from a common ancestor between us and modern primates, would it show up in an animal’s DNA? Scientists say yes. Genes encoded for ethanol metabolism are prevalent in mammals that eat fruit and nectar. In fact, humans, chimpanzees, bonobos, and gorillas share a mutation in a gene that improves an ethanol enzyme by 40 times.

What benefits this gene ultimately provides to animals remains to be researched, but access to extra calories likely gave them an evolutionary advantage in an environment where finding calories is labor intensive.

“Since positive selection in these genes encoding ethanol metabolism has been prominent among mammalian species that more commonly consume fruits and nectar, natural consumption of fermented carbohydrates is likely to be more widespread than ‘we don’t currently think so’, conclude the authors.

Have you watched our new videos on Youtube? Subscribe to our channel!

–