Monkeys' Love For Boozy Fruit Explains Why Humans Like Alcohol

The strong aversion to ripe fruit that some primates have might explain why the human species is so fond of booze.

When experts in Panama studied the diets of black-handed spider monkeys, researchers discovered that the palms these animals consume routinely contain minor amounts of ethanol.

Ethanol-specific compounds were found in urine samples from two of the spider monkeys, indicating that the alcohol isn't merely passing through their systems, but is being metabolized and used in some way.

Primatologist Christina Campbell of California State University has said that they have been able to demonstrate without a reasonable doubt that indigenous monkeys ingest ethanol-containing fruit in the absence of human intervention

In the year 2000, UC Berkeley scientist Robert Dudley proposed the intoxicated monkey theory. It claims that monkeys' great aversion to the taste and smell of alcohol is an evolutionary adaptation that permits them to chase down ripe, stimulating fruits and devour them before most other species.

The human species nonetheless has a need for ethanol, but it has been separated from the nutritional advantages of the complete fruit. Instead, people have evolved to extract spirits, and our primate ancestors' once beneficial desire for booze, has now become a threat to our health.

It's an intriguing theory, but the data showing it has been sparse and primarily anecdotal up to this point. For example, wild chimps (Pan troglodytes) have indeed been recorded consuming matured sap from the palm trees, which was later shown to have an alcoholic concentration of about 7%. However, it's unclear if the ethanol is luring the chimpanzees to the fruit or if they're getting intoxicated as a result of it.

The study conducted in Panama is the first to directly evaluate monkeys' consumption of alcoholic fruits.

The scents of mature fruits containing ethanol had previously been demonstrated to be sensitive in caged spider monkeys, but this is the first study to reveal preferential ingestion of those berries in the forest.

Not only do spider monkeys seem to consume a diet of ethanol-containing fruit, but they often show to be metabolising the fermented carbohydrates.

It's possible that people have a similar proclivity. In fact, spider monkeys consume the very same fruits that indigenous groups of humans in Central and South America use to manufacture chicha, a brewed alcoholic drink.

It's possible that the appeal of this drink stems from our need for ripe fruit. When yeast consumes sugar, it generates alcohol, which is most likely a defence mechanism against other competitors. The odour of the volatile molecule then drifts through the air, luring animals to the tasty treat.

The more ripened fruit we consume, the more vitality we get and, perhaps, the more inebriated we become.

Nevertheless, Dudley believes there is minimal inebriation among spider monkeys. The study discovered barely a fractional percentage of ethanol in the chewed up apples they analysed.

If alcohol had any evolutionary benefit, you'd anticipate it to turn up in an animal's DNA after being passed down for millions of years from such a common ancestor between humans and current monkeys.

Ethanol conversion genes are found in abundance in animals that consume berries and pollen. Humans, chimps, gorillas, bonobos, all have a genetic variant that increases an alcoholic enzyme by a factor of 40.