Originally our ancestors could not drink alcohol as we could not break it down. However, this all changed about 10 million years ago when we had a mutation in an enzyme called alcohol dehydrogenase that increased our ability to break down alcohol by 40-fold.
The reason why we had this mutation is now understood. Around 10 million years ago the world was in crisis, with global cooling causing an extinction of approximately 30 percent of all series. At that time our ancestors were ‘fossil apes’ that were living in both Africa and Eurasia. By 10 million years almost all of the apes in Eurasia became extinct, but there is some evidence that, before this happened, some of these apes returned to Africa where they evolved into humans as well as the African Great Apes (chimpanzee and gorilla). When our ancestors returned to Africa, they continued to find a cooler, dry environment where food was still scarce. At that time the mutation occurred, and it provided a survival advantage as it allowed our ancestors to eat fallen, ripe fruit that was actively fermenting. This way they could get the calories from the sugar (fructose) that was still present in the fruit, as well as generate some calories from the metabolism of alcohol itself.
The mutation thus allowed us to survive by allowing us to eat fermenting fruit that we would not have otherwise been able to eat. Today, this mutation allows us to drink alcohol, and this has paved the way to alcoholism. We are not alone— if you buy a drink for a gorilla or chimpanzee, they can also metabolize the alcohol like us. So remember this next time you are in a bar, so you are not surprised who is sitting next to you.
References
- Carn, D., Lanaspa, M.A., Benner, S.A., Andrews, P., Dudley, R., Andres-Hernando, A., Tolan, D.R. and Johnson, R.J. (2021) The role of thrifty genes in the origin of alcoholism: A narrative review and hypothesis. Alcohol Clin Exp Res. 45: 1519-1526
- Carrigan, M.A., Uryasev, O., Frye, C.B., Eckman, B.L., Myers, C.R., Hurley, T.D. and Benner, S.A. (2015) Hominids adapted to metabolize ethanol long before human-directed fermentation. Proc Natl Acad Sci U S A 112: 458-463.