These Monkeys' Taste For Boozy Fruit Could Explain Why Humans Love Alcohol, Too

The deep-rooted affinity some monkeys show for ripe fruit could explain why our species has a penchant for alcohol.

Black-handed spider monkeys in Panama eat palm fruits that contain small amounts of alcohol.

Two of the spider monkeys had urine samples that showed the alcohol was being utilized in some way.

For the first time, we have been able to show, without a shadow of a doubt, that wild primates consume fruit with alcohol in it.

This is just one study, and more needs to be done, but it looks like there may be some truth to that theory.

The drunken monkey hypothesis was first put forward by Robert Dudley. It claims that the smell and taste of ethanol is an evolutionary advantage that allows monkeys to hunt down ripe fruits and eat them before other animals can get to them.

Our own species still has a hankering for the stuff, but it is no longer related to the benefits of the whole fruit. Humans have learned to distill spirits, and the once beneficial appetite for alcohol seen in our primate ancestors has now become a danger to our wellbeing.

The evidence for this hypothesis has been limited and anecdotal. Chimpanzees have been found to have eaten palm trees' fermented sap, which has later been found to contain 7 percent of alcohol. It is not clear whether the alcohol is drawing the chimps to the fruit or if they are actually getting drunk.

The research done in Panama is the first of its kind.

The first study to show preferential consumption of ripe fruits that contain ethanol was done by spider monkeys, who have previously shown sensitivity to odors.

Spider monkeys seem to eat a lot of fruit that contains alcohol and ferments sugars.

Campbell says the monkeys were likely eating the fruit for the calories.

They would get more calories from fruit that was fermentable. The higher calories give you more energy.

A similar propensity could also exist in humans. The same fruits used by indigenous human populations in Central and South America to make chicha are also eaten by spider monkeys.

Our craving for ripe fruit may be the reason for the drink's popularity. Alcohol is produced when yeast feeds on sugar. The compound in the air draws animals to the snack.

The more fruit we eat, the more energy we get and the drunker we get.

Dudley thinks there is little inebriation in the case of spider monkeys. The researchers only tested fruits that were partially eaten.

Dudley says that they are probably not getting drunk because their guts are filling before they reach inebriating levels.

It is providing some benefit. There may be an anti-microbial benefit within the food that they are consuming, or the activity of the yeast and the microbes may be predigesting the fruit. You can't rule that out.

If there is an evolutionary advantage to alcohol, you would expect it to show up in an animal's genetic makeup.

And it does. Humans, Chimpanzees, bonobos, and gorillas all have a variation in a gene that improves an alcohol metabolism.

It's not known what benefits that gene gives animals, but it's likely that they got an evolutionary edge by accessing extra calories.

The authors conclude that positive selection on those genes that are involved in the production of ethanol catabolism has been substantial among fruit- and nectar- consuming mammals.

The study was published.