Humans have been consuming ethyl alcohol — ethanol — for millions of years. Indeed, the ability to consume alcohol may have shaped primate evolution.
Humans have this ability because, in addition to obvious beverage sources, alcohol is present in many common foods such as bread and other bakery products, fruit and fruit juices (Gorgus, et, al). Their concentrations are not as high as in beer, wine andspitits, but are present in amounts that may interfere with a breathalyzer test.
Paleogenetic science has shown that hominid ancestors of modern primates and humans were able to metabolize ethanol (turn it into food energy) as long as 50 million years ago — long before human-directed fermentation was developed.
Natural fermentation occurs when yeast — which is nearly ubiquitous in the environment — settles on fruit of all kinds. The tiniest of skin blemishes that release liquid is all that yeast needs to start metabolizing sugar, and producing ethanol as a waste product.
About 10 million years ago: Coming down from the trees
In a distant time, hominids lived in the branches of trees where they were safe from predators and fruit was abundant among the branches.
Scientists believe that over-population, major climate change and predators who learned to climb may have forced most hominids to the ground
The paleogeneticists who authored this major 2015 study — “Hominids adapted to metabolize ethanol long before human-directed fermentation” — wrote that the descent “occurred at approximately the same time as a major climatic shift known as the middle Miocene climatic transition.
This rapid environmental change brought about many large-scale ecological transitions, including replacement of Miocene forest ecosystems of East Africa with fragmented forests and grassland ecosystems, and coincided with a wave of extinctions.”
The middle Miocene, according to most sources, started about 14 or 15 million years ago.
Down from the trees and into lots more fruit
Significantly, those journal authors “identified a single mutation occurring ∼10 million years ago that endowed our ancestors with a markedly enhanced ability to metabolize ethanol.
Evolution proceeds via genetic changes and mutations. Those changes that favor survival are passed on to future generations. This is called adaptation.
As a result of genetic adaptation, early hominids who were able to metabolize fruit alcohol into food energy gained a Darwinian advantage over those who did not.
The ability to metabolize alcohol depends on a variety of Alcohol Dehydrogenase (ADH) enzymes. Enzymes are a type of protein with specific cellular tasks.
These ADH enzymes are vital because a toxic carcinogen is produced during the first step of alcohol metabolism. That chemical is called acetaldehyde.
Acetaldehyde is also present in many non-alcoholic staples of human existence:
- milk, yogurt, cheese and other dairy products,
- bananas, strawberries, apples, oranges and other fruit,
- vegetables ranging from carrots, garlic tomatoes, onion and peas,
- beverages such as coffee, tea and soft drinks
This table, from the study linked above, offers a much more detail.
Another study noted that acetaldehyde is found in , fermented and pickled vegetables and drinks such as kombucha.
Finally, acetaldehyde is added to many foods because the U.S. Food and Drug Administration considers it an ingredient that is “Generally Recognized As Safe (GRAS). (use CTRL+F to search the list)
Tobacco smoke — NOT GRAS — also contains acetaldehyde
Fortunately for human existence, acetaldehyde doesn’t remain toxic for very long before it is neutralized by the ADH family beginning with ADH4 which is found in the mouth, esophagus, and stomach.
There are several forms of ADH, and each has several different genetic forms. These different forms are called polymorphisms.
An individual’s ability to metabolize ethanol will depend upon which variations and their combinations are present in their genes.
“Ethanol metabolism is complex and involves other ethanol-metabolizing enzymes [e.g., ADH1, ADH2, and the microsomal ethanol oxidizing system (MEOS)], enzymes involved in the downstream metabolism of by-products from ethanol metabolism (e.g., ALDH2, which oxidizes acetaldehyde created from ethanol), and enzymes indirectly affected by the by-products of ethanol metabolism (e.g., ALDH1). ” — Carrigan et. al.
That study reported that about 10 million years ago one these enzymes emerged that was 40 times more effective at metabolizing ethanol.
That enzyme — ADH4 (alcohol dehydrogenase class IV) — is one of the primary ADH enzymes because it is
According to the 2015 study authors, those with efficient ADH4 reproduced faster and survived food shortages best.
“This change occurred approximately when our ancestors adopted a terrestrial lifestyle and may have been advantageous to primates living where highly fermented fruit is more likely.”
Not coincidentally, fruit on or near the ground will contain more ethanol than hanging fruit.
This may be because that the environment is moister close to the ground and fruit is more likely to have skin breaks from falling, contact with branches that directly. exposes the sugars within.
Excellent further reading