Many people enjoy a nice glass of beer or wine after a long day at the office. But ever wondered when we evolved the capacity to process alcohol? Currently, there are two hypotheses. The first one states that alcohol then entered our diet when humans began to store food and subsequently developed the ability to ferment food about 9000 years ago. The alternative hypothesis puts the date back to as far as 80 million years when primates ingested alcohol through their frugivorous diet. To settle this debate, Matthew Carrigan (Santa Fe College) and his colleagues explored the evolutionary history of ADH4, an enzyme that plays a crucial role in alcohol metabolism.
Just Try It!
The evolution of the ADH4-enzyme revealed an important event about 10 million years ago, namely one change in the amino-acid sequence at position 294 (Alanine became Valine). To test the effect of this mutation, they synthesized the ancient enzyme using bacteria. The comparison between the ancient enzyme (from before the mutation) and the current one showed that the mutation led to a 40-fold increase in alcohol-oxidizing capacity. Clearly, the mutation had a positive effect on ADH-4.
But things get even more exciting! The mutation occurred 10 million years ago, which coincides with the Middle Miocene Climatic Transition (MMCT) when several large-scale ecological changes took place. In East-Africa, for example, the forest ecosystems were replaced by grasslands and savannas. Primates were forced to leave their safe trees and explore a terrestrial lifestyle. This included eating fruits that have fallen from the trees. These fruits ferment more quickly, leading to a higher alcohol consumption by the primates. Animals with the new and improved ADH4-enzyme would benefit from this addition to their diet. An adaptive advantage.
I can already imagine a family of early primates walking through the grasslands and finding some fermenting fruits. The kids look at them in disgust. But the mother hands out the fruits and gives her offspring a look that says: “Just try it!” A few bites later, they are hooked on the stuff. And another 10 million years later (give or take a few years) I am sipping from a nice Belgian beer. Thanks for trying it, little guy!
Apart from the great story, this study also provides “evolutionists” with some important arguments against creationists. Although I promised myself not to discuss creationism-related issues on my blog, I briefly want to address two creationist arguments that are refuted by this study. Firstly, creationists say that evolution cannot be tested experimentally, it is a historical science. This study clearly performed an experiment to show that the mutation had a beneficial effect on the ADH4-enzyme. And this brings me to the second argument, namely that mutations are never beneficial. Well, a 40-fold increase in efficiency? Need I say more… I guess they will flush out the disappointment with some alcohol (and probably forget). Cheers!
Carrigan, M., Uryasev, O., Frye, C., Eckman, B., Myers, C., Hurley, T., & Benner, S. (2014). Hominids adapted to metabolize ethanol long before human-directed fermentation Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1404167111