Is drinking in our genes?

The recent observation of chimpanzees indulging in palm “wine” has lent weight to a study suggesting hominids evolved the ability to metabolise alcohol 10 million years ago.

A 17-year study has shown a troop of chimps in the West African country of Guinea to be regular topers of newly fermented palm sap, occasionally drinking enough to show “visible signs of inebriation”.

Collecting this palm “wine” is common among the locals but scientists led by Dr Kimberley Hockings from Oxford Brookes University and the Centre for Research in Anthropology in Portugal noticed that chimpanzees were partial too with some individuals drinking up to 85ml of alcohol – 8.5 units or a bottle of wine – in a sitting.

Although other animals are known to get drunk on naturally fermenting fruit, alcohol is generally toxic for most and a significant quantity is enough to kill them.

The chimpanzees however seem perfectly unaffected in the long-term, returning regularly to drink the palm juice which is generally 3% abv but ranges as high as 7% at times.

Some display more of a taste for it than others and can appear to be “drunk”, acting in an agitated manner and falling asleep, but aside from waking with (one must suppose) a hangover brought on by dehydration they appear able to metabolise the alcohol as humans do.

The team’s findings were corroborated by other scientific groups which had observed the same group over the last 20 years.

The observation has also drawn attention to a study in the US, conducted by Matthew Carrigan of Santa Fe College, which argued that: “Hominids adapted to metabolise ethanol long before human-directed fermentation.”

The study’s abstract states: “Here, we resurrect digestive alcohol dehydrogenases (ADH4) from our primate ancestors to explore the history of primate–ethanol interactions. The evolving catalytic properties of these resurrected enzymes show that our ape ancestors gained a digestive dehydrogenase enzyme capable of metabolizing ethanol near the time that they began using the forest floor, about 10 million y ago.

“The ADH4 enzyme in our more ancient and arboreal ancestors did not efficiently oxidize ethanol. This change suggests that exposure to dietary sources of ethanol increased in hominids during the early stages of our adaptation to a terrestrial lifestyle.

“Because fruit collected from the forest floor is expected to contain higher concentrations of fermenting yeast and ethanol than similar fruits hanging on trees, this transition may also be the first time our ancestors were exposed to (and adapted to) substantial amounts of dietary ethanol.”

The full study can be read here.