Why do (some) animals get tipsy?
Humans are not the only animals with a taste for alcohol. It has been described in different animals in the wild, especially mammals, that they do like to eat overripe fermented fruit, and with it experience similar effects to the ones almost all of us are familiar with.
It turns out that some mammals cannot take their alcohol as good as others, and that the reason behind it might be changes to a single gene: the ADH7.
Researchers 1 looked at the genomes of 79 different mammal species and found that this gene was rendered inactive in 10 different branches of the mammal family tree. Even though there are more than a number of genes implicated in ethanol metabolism, it seems that dysfunctional mutations to the ADH7 gene are responsible to this difference in their ability to stand ethanol consumption, most probably because it inhibits the capacity to metabolize it. And therefore increases the ethanol blood levels leading to tipsy animals.
Some mammals cannot take their alcohol
But you’re probably asking which are the unfortunate ones to carry this mutation. This (bad) luck fell independently on elephants, armadillos, cattle, rhinos, or beavers among others. On the other side of the ethanol-resisting mammals are…humans and non-human African primates.
Why can we stand so much ethanol, you say? It could be because the ADH7 was mutated in evolution to be 40 times more effective in breaking down ethanol than the typical gene version in the majority of mammals. Funnily though, tree shrews which were the ones that inspired the research do not have the same mutation as us. These super drinkers, since they can take much more alcohol than humans without losing it, have found a way to deal with ethanol that is as yet still not known.
Poor elephants, on the other hand, are on the losing side and are well-known for their like of fermented marala fruit (a sort of mango), and even in laboratory conditions do not decline a sip of the good stuff. Even though there have been ongoing discussions as to how possible it is for African elephants to eat enough fruit to get tipsy, it seems that the loss-of-function mutation in their ADH7 could be the key to their low endurance when it comes to alcohol.
So, even though there remains some unanswered questions when it comes to ethanol metabolism, it seems that the ADH7 gene might be key to understanding what makes a mammal more resilient to alcohol’s bad effects. As good as our ADH7 gene might be, let’s not forget that other genes still limit our capacity to stand alcohol. Variations to the two principal enzymes involved in ethanol oxidative metabolism alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) in Asian populations make them more susceptible to alcohol, for instance. So, please do not just go get another drink, in case you’re more of an elephant than a chimp.
- Mareike C. Janiak et al (2020) Genetic evidence of widespread variation in ethanol metabolism among mammals: revisiting the ‘myth’ of natural intoxication Biology Letters doi: 10.1098/rsbl.2020.0070 ↩