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I think, therefore I harm

Humans and Alcohol

During the next few days, if you’ve not already begun, you will enjoy alcohol. A lot of it. But why?


Alcohol is a toxic substance that we use to disinfect, as it kills germs and microbes. It’s a sure way to kill most animals and plants, and pretty much any form of life. Humans, however, developed the ability to resist alcohol and even enjoy it, a trait that we share only with a few other superior apes.

We metabolize alcohol. That is, we have organs and enzymes in our body able to decompose alcohol into simpler elements. Part of alcohol is transformed into sugar, which we are able to use for energy and store as fat. The rest is quickly filtered out of the blood stream.

drunk-catA dog, for instance, cannot metabolize alcohol. Even a small amount of alcohol will make a dog drunk for hours on ends. Alcohol, a complex substance, will only be filtered out from their body through a very long process. A moderately large amount of alcohol will likely kill the dog.

Alcohol comes in different forms. Ethanol is one type of alcohol which is produced from fermentation of sugar from fruits, and this is the type we consume. ADH4 is the main enzyme responsible for metabolizing ethanol. Present in our stomach and throat and on our tongue, it is the first ethanol metabolizing enzyme to encounter any alcohol we may ingest, and thus digestion of alcohol begins very early. ADH4 comes in different forms though, and only a small subset of these is able to metabolize ethanol efficiently.

In a study which began in early February, a team of scientists first extracted the ADH4 enzyme from different species of mammals to determine their efficiency on oxidizing ethanol. They found that three species had the ADH4 variant that had a significant efficiency: chimpanzees, gorillas and humans. Other mammals, and notably other primates, did not have the right variant. Interestingly, all of these three mammals are very close together from a genetic standpoint. The team then used the fact and correlated it with other historical knowledge to draw a complete story.

The Story

About 10 million years ago, our planet went through a major climate change which made a dramatic impact on our landscape. Many ancient species had to go through major adaptation to survive, and those that failed to adapt to the changing world went extinct. It is believed that around that time, a new branch of primates diverged from orangutans – the most arboreal of all great apes – and began spending more time on the ground. With the forests yielding place to grasslands, living an entire life in the trees was now very difficult. The new species would have walked the ground and found new sources of food.

It is believed that the new primate species would have quickly evolved a new variant of ADH4 able to process ethanol efficiently. The change would have permitted the species to eat rotten fruits from the ground, which may often have begun fermenting. The alcohol-resistant gene would have given them a major advantage, giving them the chance to eat from a food source which would have been toxic to other species when other food sources would become scarce, possibly a seasonal event. This single mutation may have saved the species from extinction.


Salt, sugar and fat are all substances that we enjoy. They were essential to our subsistence, but they were scarce. We likely begun enjoying the taste of these as a mean to ensure we would seek them and consume enough of them. However, as our world changed, we failed to adapt and now that we have too much of these, we see a notable increase in illnesses associated with abuse of these substances. The same applies to alcohol. We likely evolved to enjoy alcohol as using it inferred a notable advantage: the ability to ingest food that was toxic to others in periods of scarcity. Alcohol was rare, but soon after we begun agriculture, about 9000 years ago, we begun fermenting fruits to produce alcohol, and eventually distilling it into pure alcohol. A sudden increase of alcohol in our wold led to many illnesses linked to the substance, such as alcoholism and cirrhosis.

The team who focused on the aforementioned study was mainly interested in how alcohol came to us and its effects on our world. Though they believe that being able to metabolize a small amount of ethanol was an advantage to us millions of years ago, they believe that the recent increase of the substance in our world didn’t let us enough time to adapt to consumption of large amounts of alcohol, which explains the resulting illnesses.

They believe that rotten fruits were not a first choice for our ancestors, which rather consumed them when their first choice of meal was infrequent. Our ancestors thus never adapted to a life of daily alcohol consumption.

During the festivities which just begin, please enjoy your drinks like our ancestors did. But do it safely and moderately. And please, remember that we never evolved to drive under the influence of alcohol. Enjoy your holidays and return to us safely in 2015.


8 comments on “Humans and Alcohol

  1. sledpress
    December 23, 2014

    I remember noting some time back that evolution was apparent even through historic times as some communities of humans developed alcohol while others did not. People from the Fertile Crescent (even before Islamic prohibitions) seem far less susceptible to habitual drunkenness than people from areas where fermentation and distillation were understood later in historical times, and of course North American Indians can hardly withstand the stuff at all, having lost that critical enzyme. One assumes that hardcore drunkards were less likely to pass on their genes in the populations that had plenty of booze around.

    • Tom Duhamel
      December 23, 2014

      I may have failed to mention the difference in tolerance among ethnic groups. You are absolutely right regarding the Natives, so much that alcohol is banned from many communities, including the entire Nunavut territory. Asians are also not especially known for their tolerance to alcohol. While ADH4 is recognized as the main factor, the team of researchers admitted that there must be more to discover about this.

      Have a good time, my friend!

      • sledpress
        December 23, 2014

        My Irish liver and I plan to do so.

  2. heretherebespiders
    December 26, 2014

    Interesting – I know elephants will steal beer from humans in Africa, and birds will feast on fermenting berries, and over here I learned that badgers get drunk on rotting damsons (a type of small plum). Wonder how they learn to do this?

    • Tom Duhamel
      December 26, 2014

      I really don’t know. I saw a documentary years ago about different animals in a certain area of Africa which gather together under a certain tree at a particular time of the year because they know the rotten fruits at the base will make them drunk. Rotten fruits are a very low alcohol content, but with little tolerance they sure get affected quickly. Why do they enjoy it? What would be the purpose in evolution? It’s clearly not for survival.

      • heretherebespiders
        December 26, 2014

        It just seems very … human to want to alter your state. Kind of proves they know the difference, doesn’t it?

        • Tom Duhamel
          December 26, 2014

          Alcoholism is a known condition in dogs. I was once a guest at someone whose dog would come at a certain smell. He would wait for his master to give him his toke. He would then lay down for a couple of hours. He obviously liked it, and I was shocked because I didn’t know any animal could like to alter its state. I don’t have answers, but I know we’re not alone.

          • heretherebespiders
            December 26, 2014

            I never gave any of my dogs much booze, but before we had my heart dog put to sleep we took him to the pub and let him have as much Guinness as he wanted. It wasn’t much, as he was so poorly and also full of the steak we gave him, but I hope it helped. He did love Guinness.

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This entry was posted on December 23, 2014 by in History, Holidays, Society and tagged , , , .
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