Humans have a long societal and evolutionary history with alcohol. Studies have shown that alcohol metabolizing systems appeared in our primate ancestors long before humans ever existed, between seven and 21 million years ago.
Researchers from California State University released a new study on this fascinating topic that supports the “drunken monkey” hypothesis. They concluded that the animal’s alcoholic tendencies came about because of the nutritional values of fermented fruit.
Drinking for their health?
The study focused on the behavior of black-handed spider monkeys (Ateles geoffroyi) in Panama, studying the properties of discarded eaten fruit of the primates. Alcohol concentration was between one to two percent by volume in this food, created as a natural by-product of fermenting yeast.
Urine samples of the monkeys revealed the metabolites of alcohol, meaning broken-down versions of alcohol molecules. This proved the animals were processing the ethanol rather than just letting it pass through their bodies untouched.
Consuming fruit with higher levels of alcohol means a higher number of calories ingested, resulting in more energy obtained. Scientists have also suggested there may also be an antimicrobial benefit to this diet and the predigested nature of the food could have a perk in saving energy during digestion.
“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,” explained Christina Campbell, lead author of the study.
They continued: “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.”
Some species of primates have been shown to consume fruit with an alcohol content of up to eight percent. Although, scientists say it’s likely the animals aren’t getting drunk from eating the fruit as their guts would fill up before they eat enough to feel intoxicated.
This study allows contemplation of the role of alcohol in primate diets, which might have led up to human enjoyment, and sometimes overindulgence, of the substance. “Human ancestors may also have preferentially selected ethanol-laden fruit for consumption, given that it has more calories,” Campbell said. “Psychoactive and hedonic effects of ethanol may similarly result in increased consumption rates and caloric gain.”
As it turns out, there may be an evolutionary primate disposition toward alcohol, something that might come into scientists’ consideration of nutrition or even the treatment of alcoholism.
Source study: Royal Society Open Science – Dietary ethanol ingestion by free-ranging spider monkeys (Ateles geoffroyi)