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As a parent of older teenagers, one question that sometimes comes up in my house is why humans have such fondness for alcohol, despite its sometimes unpleasant after-effects.
New research has lent support to an explanation called the “drunken monkey” theory. This says that millions of years ago, our primate ancestors grew a liking for alcohol’s smell and taste, because it is found in ripe fruits, as they start naturally fermenting.
The idea was originally put forward in a 2014 book, The Drunken Monkey: Why we drink and abuse alcohol, by Professor Robert Dudley, a biologist at UC Berkeley in California, although it is not yet universally accepted.
While it might seem like alcohol is a highly unnatural substance for us to consume, in fact it is widely found in nature, Professor Dudley pointed out.
That’s mainly thanks to the existence of fruit. Around 100 million years ago, plants started packaging their seeds inside tasty and calorific fruits, so they would be dispersed by animals.
Sugar is the main attraction. But in very ripe fruit, yeast found in the environment may start feeding on that sugar, breaking it down into alcohol in the process.
Alcohol is a smaller and lighter molecule than sugar so it floats into the air. In hot and humid rainforests, above a tree laden with ripe fruit there will be an “ethanol plume”.
This could be an olfactory signpost for troops of monkeys, said Aleksey Maro, a primatologist and colleague of Professor Dudley’s. “When you’re making your way through a sea of green to find the few globs of calories hanging in the trees, even a small advantage can be very major.”
It could even reveal which kind of tree is releasing the plume, because ethanol reacts with other complex molecules within the fruits, which vary with the species. “Ethanol is this broad, non-specific signal, and the closer the animal gets to the source of fermentation, the more layers there are of these smells,” said Maro.
Initially there was scepticism about the drunken monkey theory, because most scientists thought primates lacked a taste for booze and that it was rare for them to eat fruit that is overripe.
Alcohol has become important for social bonding among many humans (Photo: Azman Jaka/Getty)Monkeys feasting on boozy fruit
It is difficult to investigate because it would be unethical to give wild or captive primates alcohol, said Dr Kimberley Hockings, a chimpanzee expert at the University of Exeter.
But as primatologists looked out for it, there were increasing reports of monkeys and apes feasting on fruit that had started to ferment.
Dr Hockings, for instance, has documented wild chimps eating fermenting breadfruit and sometimes sharing it with each other.
These could have been unusual cases. So, in the latest study, Maro’s team investigated how much alcohol there is in chimps’ typical daily diet.
At two different sites where wild chimps live, in Uganda and Ivory Coast, they recorded which fruit species the animals ate, and the quantities, and measured their alcohol content.
Maro even sampled one of the fruit species – the African star apple. “It had a sourness to it, but it was also very sweet, as it’s 20 per cent sugar,” he said. “It was delicious.”
They found that chimps are consuming about 14 grams of ethanol a day on average, which would be equivalent to a human having two glasses of wine. The research was published in the journal, Science Advances.
It doesn’t mean the chimps were getting drunk, not least because the booze was spread out over the whole day and consumed with food. But it does support the idea that alcohol is a routine part of their diet.
Chimps can use alcohol as an energy source, as can people. Indeed, an enzyme that breaks down alcohol changed to become much more efficient in our primate ancestors about 10 million years ago, it was discovered earlier this year.
Humans split from the lineage with chimpanzees about six million years ago.
At the time when the upgraded alcohol enzyme appeared, our ancestors had begun spending less time in the trees and more time on the forest floor, which ultimately led to walking on two legs.
Fruit that is found on the floor is more likely to be overripe and fermenting. So, there may have been even more alcohol in our diet during this pivotal period.
Long history of use
Seen in light of this evolutionary history, it now becomess less surprising that most modern-day humans – although not all – are partial to a drink.
There is evidence that people have been deliberately fermenting fruit or grains to make alcoholic drinks since around the start of farming 10,000 years ago.
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Of course, our history with alcohol doesn’t mean we should feel free to drink as much as we want of it today.
“We have these liquid, highly concentrated dosages that we are able to consume in a very short period of time. That’s completely unnatural for wild animals,” said Maro. “Maybe that’s why humans today have so much trouble with alcohol.”
On the other hand, perhaps getting drunk reflects a different aspect of our nature – the urge to take mind-altering drugs, said Dr Lorenzo Stafford, a psychologist at the University of Portsmouth.
“Pretty much every civilization that’s ever been has consumed some sort of drug, whether it’s alcohol, tobacco, cannabis, or cocaine, from the Egyptians to the Aztecs,” he said. “The urge to alter our consciousness is part of the human condition.”
Rising obesity rates are widely viewed as the biggest health crisis facing the Western world. Prevention is better than cure, so doctors are focused on stopping children from getting overweight.
Many countries have programmes aimed at parents of young children, such as healthy eating sessions, exercise groups, and advice on weaning foods and screen time. There’s just one problem: none of it is effective.
I’ve been watching
Department Q is a brilliant new crime drama on Netflix. At first you think it will be yet another series featuring a grumpy cop with psychological scars, but make sure you watch to the end of the first episode. Then, things take a more interesting turn.
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