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THE bar fly gently raises his throbbing head. Woken from his drunken stupor,
he casts a bleary eye around the room. Something is not quite right.

Sitting on a stool to his left, a chain-smoking gorilla stares mournfully
into a pint of beer, while three fruit flies play leapfrog around the rim of the
glass. In one corner, a troop of male baboons is knocking back tequila slammers
and arguing noisily about who has the shiniest backside. And above the bar,
hanging upside down from the rafters, three fruit bats are drinking sangria
through a straw. One of the bats loses its grip and falls to the floor in a
heap.

Clearly, it is time to leave.

A night out at the pub can reveal the animal in all of us. And with good
reason. Drunkenness has a natural history that goes way back, long before the
Dog and Duck or the White Horse first opened their doors. Our fondness for
alcohol, far from distancing us from the animal kingdom, merely confirms our
place within it. Every time we walk into a bar, we are simply retracing our own
evolutionary steps. That, at least, is the view of Robert Dudley, an
evolutionary biologist from the University of Texas at Austin. “Nobody has come
at this from an evolutionary standpoint before,” he says. “I’m convinced
something fundamental is going on.”

Dudley believes that the origins of our love affair with alcohol date back to
the time when we first began dining on fermenting fruit. Millions of years ago,
when copious body hair was still in vogue, our ancestors would have spent most
of their daylight hours scouring the forests for ripe fruits, rich in nutritious
sugars, just as monkeys, apes and other fruit-eating animals do today. Fruit
sugars will also attract the attention of the local yeast population, so it is
inevitable that a diet of ripe fruit brings with it a side salad of ethanol. But
ethanol is much more than an addictive intoxicant. For a hungry animal, it is a
valuable source of energy.

Ripe fruits are a relatively scarce resource in the rainforest. Trying to
find one among all those leaves isn’t easy. But clues to their whereabouts can
come from the ethanol inside them. Because ethanol is a highly volatile organic
compound, ripe fruits will ooze a trail of ethanol vapour. To find the fruit,
all you need is a nose, or antennae, sensitive enough to sniff out the trail.
According to Dudley, this is where our bond with alcohol may really have begun
to strengthen. He believes that, just as the scent of alcohol attracts fruit
flies and butterflies, evolution may have co-opted ethanol into our repertoire
of olfactory stimulants. An evolved sensitivity to an alcoholic vapour trail
would lead an animal straight to the nutritional prize, with the ethanol itself
making up a significant part of the energy reward.

If Dudley is right, evolution forged an allegiance between our senses and our
physiology, and we have been predisposed to alcohol ever since. In fancy
biojargon, we developed a “sensory bias” towards alcohol. Getting drunk,
therefore, became an occupational hazard, a simple consequence of unwittingly
feeding on an especially ripe batch of fruit.

There is no doubt that many animals have the physiological capacity to get
drunk. But in the wild, it is usually only the fruit-eaters who are ever
presented with the opportunity. We should see similar kinds of behaviours in all
animals that eat fruit, according to Dudley.

There is certainly no shortage of stories about animals getting drunk in the
wild. At the end of the summer, for example, worker wasps and hornets feast on
fermenting fruit. Postprandial flights often take on a surreal air and
collisions with trees are a likely outcome. Similarly, birds pay little
attention to the “don’t drink and fly” slogan. Whether it is waxwings and robins
in the US harvesting a crop of overripe berries, or lorikeets in Australia
feeding on fermenting nectar, wing-to-eye coordination rapidly evaporates as the
birds fly headlong into walls and windows, or fall from their perches. And a
yellow-bellied sapsucker—a kind of woodpecker—is said by one
bird-watcher to have become so confused after a sip on some potent sap that it
mistook his trouser leg for a tree trunk.

Over in Africa, there is that most terrifying of creatures, the inebriated
bull elephant. With a belly full of fruit from the favoured marula tree, and
some elephantine gulps of water, the elephant’s stomach becomes a giant
fermenting vat, turning a normally placid beast into the hell-raiser of the
savanna. Behind the bushes, giraffes struggle to stand up on their stilted legs,
while monkeys and apes drift off to sleep in the afternoon’s alcoholic heat
haze. Wherever you look in the animal kingdom, there are fruit-eaters getting
sozzled.

But what of the fabled drunk skunks and newts? How do they fit into the
alcohol and animals picture? Not too well, according to the experts. Jerry
Dragoo, a skunk specialist from the University of New Mexico pours cold water on
the intoxicated skunk idea. “It’s a rhyming thing,” he says. It is intriguing,
however, that the same phrase is used in Brazil, in non-rhyming Portuguese.
Skunks do, at least, include fruit as part of their varied diet. Perhaps someone
once saw a skunk behaving badly.

Newts, on the other hand, like all amphibians and reptiles, are hard-core
carnivores. So how did their drunken reputation come about? Verina Waights, a
newt expert from Britain’s Open University admits that there is a mini-cottage
industry of explanations, but offers her own personal favourite. “Juvenile
stages have been found floating in barrels of beer,” she says. When larval newts
metamorphose, the young adults leave their pond in search of a new aquatic home.
Sometimes, it seems they mistake a beer barrel for a new aquatic residence. But,
she adds, “there’s no evidence they seek out fermenting fruit”.

It is in the fruit-eaters that Dudley believes we will find the secrets of
our own predilection for alcohol. He turns up the speculative heat about our
boozy origins with some intriguing observations on our own drinking habits.
“Walk into a bar and have at look what people are drinking,” he says. “People
tend to drink dilute concentrations of ethanol—beer and wine. Even when
you get high concentrations [spirits], it’s nearly always diluted.” Even at
their metabolic peak, fermenting yeasts can only produce alcohol until their
surroundings contain 10 to 15 per cent ethanol. Is it more than a coincidence
that the dilutions of alcohol we prefer today are the same ones our hairy
ancestors would have encountered in the forests? “It makes sense in terms of
what we are evolutionarily predisposed to,” says Dudley.

And where, Dudley asks, does our liking for those ridiculous fruit liqueurs
come from? Is it possible that these drinks are ruthlessly exploiting a sensory
bias we have developed towards fruit smells and ethanol?

It certainly seems as if the bar fly’s sensory bias has been well and truly
exploited. Lurching off his stool, he staggers out into the street and collapses
in the gutter. On the opposite side of the road, a young boy tugs at his
mother’s arm. “Don’t stare, Timmy,” his mother says, “they’re just animals.”
She’s right, of course. Alcohol is in the blood.

IT is remarkable how progressive levels of drunkenness produce such similar
behaviour in different creatures, even those as distantly related as humans and
fruit flies. Initially, like humans, flies become twitchy and hyperactive. This
is followed by an uncoordinated phase, when accurate movements become
problematic. And finally, there is the moment that brings even the best party to
a close—sedation.

But while all animals might follow a similar path to inebriation, the amount
of alcohol it takes can vary enormously from person to person—and from fly
to fly.

For over a decade now, biologists have been using an ingenious device known
as the “inebriometer” to test ethanol sensitivity of fruit flies, in efforts to
identify genes behind the differences in alcohol tolerance. The inebriometer is
a tall glass column with internal baffles for the flies to sit on. Before any
ethanol is added, the flies sit on the highest baffle, bright-eyed and bushy
tailed. Then a tap is turned and ethanol vapour flows through the column from
top to bottom.

When the flies become floppy and comatose, they lose their grip and drop from
baffle to baffle, eventually falling out of the bottom of the column. The time
it takes for the flies to be “eluted” gives an accurate measure of their ethanol
tolerance. One genetic mutation that seems to increase the flies’ alcohol
sensitivity has been picked out as a result of this screening process. This
quick-to-drop fly mutant has been aptly named “cheapdate”.