Hominids adapted to metabolize ethanol long before human-directed fermentation

Ancestors’ taste for booze 10m years old

A study has suggested that evolution is to blame for our love of alcohol, with a single gene mutation that occurred 10 million years ago endowing our ancestors with the ability to break down ethanol.

Researchers from Florida have claimed that long before humans learnt how to ferment fruits into alcohol, their guts had evolved in order to metabolise and digest alcohol, paving the way for 10 million years of imbibing, as reported by nbcnews.com.

Matthew Carrigan, lead author of the study and a paleogeneticist at Santa Fe College in Gainesville, Florida, said: “A lot of aspects about the modern human condition — everything from back pain to ingesting too much salt, sugar and fat — goes back to our evolutionary history. We wanted to understand more about the modern human condition with regards to ethanol [alcohol].”

Carigan’s team studied a group of digestive enzymes called ADH4 which are found in the stomach, throat and tongue of primates. Taking the ADH4 genes of 28 mammals, scientists investigated nearly 70 million years of primate evolution pinpointing the presence of ADH4 in relation to when their lineage diverged with humans.

The enzyme was first found plentifully in the gorilla, a primate ancestor whose human lineage diverged roughly 10 million years ago, indicating that a single genetic mutation 10 million years ago was responsible for giving humans the ability to break down ethanol.

The timing of this mutation coincided with early hominids choosing to live on the ground rather than in the trees, which the team suggested could have occurred to help early humans make the best out of rotting fruit that had fallen onto the forest floor.

Carrigan said: “I suspect ethanol was a second-choice item. If the ancestors of humans, chimps and gorillas had a choice between rotten and normal fruit, they would go for the normal fruit. Just because they were adapted to be able to ingest it doesn’t mean ethanol was their first choice, nor that they were perfectly adapted to metabolize it. They might have benefited from small quantities, but not to excessive consumption.”

While humans may have been ingesting alcohol for 10 millions years, human are only thought to have developed ways to intentionally ferment fruit some 9,000 years ago.

Releasing their findings, researchers said: “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 study was published this week in the Proceedings of the National Academy of Sciences journal.