Why some animals such as armadillos and beavers get more easily drunk than others
Reports of drunken animals have been around for a long time, but only now do we have scientific proof that some animals can indeed get drunk. This is due to a gene that is responsible for breaking down alcohol.
A small number of animals, among them bovids (cattle and sheep), carnivores (dogs, foxes, sea lions and walruses), horses, cetaceans, elephants and armadillos are affected by the breakdown of the ADH7 gene during their evolution. This makes it harder for their bodies to break down ethanol. This particular gene might allow ethanol to build up in their bloodstreams.
Fruit is generally not a part of these species’ diets. They live of meat, grains or leaves instead. But every now and again some of them will feast on rotting fruit showing signs of inebriation shortly afterwards.
The drunken elephant myth is not a myth
A good example are elephants who have been reported to get drunk on fallen fermenting marula fruit. For a few years these reports were classed as myths by scientists as it was assumed that there would not be enough alcohol in the fruits to impact a massive elephant in such a way. They extrapolated from human physiology that the amount an elephant would need to consume was impossible. What has now come to light, though, is the fact that elephants might have a much lower tolerance for alcohol because of the inactive ADH7 gene.
The study was, however, inspired by small rodents with an enormous tolerance for alcohol. Malaysia’s pen-tailed tree shrews feast on betram palm flowers containing a very high concentration of alcohol. Nevertheless, they show no sign of intoxication.
The same is true of many types of bats who feast on fermented fruit on a regular basis. Studies have shown that it does not affect their ability to fly or to use their echolocation to navigate.
What about humans?
Humans as well as non-human African primates have evolved with a much more efficient ADH7 gene. It has shown to be about 40 times better at breaking down ethanol than other mammals. Interestingly, the tree shrew does not boast this amazingly efficient gene, so it is unknown what causes their resistance to alcohol intoxication.
The change in our DNA evolved roughly 10 million years ago in an ancestor we share with the great apes. This was a very long time before we started to create alcohol intentionally through fermentation. Our ancestors began brewing only about 12000 years ago. Scientists believe that the change in our genes could be the result of switching to a more terrestrial lifestyle where we encountered and started to enjoy more fallen fruit. Some fermenting fruit is surprisingly high in alcohol reaching levels of up to the strength of a pale ale.
When considering the diets of mammals and their metabolism it is important to look at the history of each species and not extrapolate from humans as each species evolved separately according to their needs.
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