We've been drinking for a long time. Archaeological evidence suggests humans in China were deliberately mixing grapes with rice to produce a fermented beverage around 7000 B.C. But scientists have theorized for several years that our thirst for alcohol goes back much further, to the prehistoric days when early humans tasted fermented fruit and enjoyed the taste—and the buzz. Now a new study by researchers in Florida and Indiana argues that we inherited a tolerance for booze from our primate ancestors, who evolved an ability to efficiently metabolize alcohol roughly 10 million years ago.
Fruit has been fermenting for as long it has existed—ripe fruit is full of sugar, delicious to yeast. Researchers have observed for years that certain animal species enjoy this fruit after it's been fermenting. The new study, co-authored by Dr. Matthew Carrigan, a paleogeneticist at Santa Fe College in Gainesville, Fla., and published online by the Proceedings of the National Academy of Sciences, is rooted in the fact that other primates besides humans possess the enzyme needed to metabolize ethanol, including chimpanzees and gorillas. His team “reverse engineered” the history of that crucial enzyme, Class IV alcohol dehydrogenases (ADH4), using genes from 28 mammal species, including 17 primates.
Armed with this information, the team then backtracked down the 70 million years of primate evolution to see how the ADH4 gene changed over millennia and when each species of primate diverged from the rest. They then tested the various ADH4 genes of the different species to see which enzymes are the most efficient.
They found that our primate ancestors' ADH4 gene mutated roughly 10 million years ago, creating a new version of the enzyme that metabolized ethanol 40 times more efficiently. In other words, those ancestors developed better tolerance for booze.
What were the benefits of being able to process ethanol so efficiently? One hypothesis for the success of ADH4 is the role it would play in the survival of those who possess it: that they would be able to better “handle their liquor” by being less susceptible to ethanol intoxication and therefore more adept at defending themselves. Then there was the ability to eat fruit that other animals could not tolerate. This would theoretically give them an advantage in the hunt for resources.
Carrigan added that the mutation dates back roughly to the time our ancestors started coming down from the trees and adopting a more terrestrial lifestyle. Fermenting fruit on the ground was an extra food source. He adds that this information might help our understanding of why we link alcohol with pleasure, specifically that the effects of ethanol intoxication were linked to this new and exclusive food source.