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Human Ancestors Thought to Be Consuming Alcohol 10 Million Years Ago

apples on the ground

Image credit: Reza via Flickr

It was previously thought that the predecessors of mankind started to imbibe alcohol nearly 9,000 years ago when the food storage and the natural fermentation process came into being. However, this idea was totally wrong!  Based on the analysis of ancient alcohol-metabolizing enzymes, it was 10 million years ago that ancestral apes began to consume ethanol, at that time they moved off from the trees and got used to a terrestrial life on the forest ground. The result regarding such study has been recently published in the Proceedings of the National Academy of Sciences.

Many current diseases are the result of the incompatibility between the today’s environment and the environment to which our genome was used. For instance, the recent increase in our sugar consumption is the cause of diabetes, hypertension and obesity. However, it would not be expected for an animal fully adapted to a sugar-rich diet to have such diseases, so it is suggested that human being simply do not have sufficient time to be adapt for this modern diet. It is the same case that a recent introduction of ethanol, which could take place just 9,000 years ago, would also demonstrate that alcoholism in modern humans could show an incomplete genomic adaption because of insufficient time. Furthermore, as confirmed by an alternative model, primates had consumed ethanol by eating fleshy fruits around 80 million years ago.

To go on a further study, Matthew Palczewski and his team from Santa Fe College were engaged in analyzing alcohol dehydrogenase class IV (ADH4), the first enzyme being exposed to ethanol through the digestive tract which could metabolize ethanol. In their investigatory efforts, Palczewski’s team regenerated ancestral ADH4 enzymes from 28 mammals of different kinds that were representatives of the various points along the last 70 million years, during which period of time primate had evolved. After that, the team made measurement of the ability of such ancient enzymes to metabolize ethanol.

As a result, the team made it sure that a single genetic mutation that happened nearly 10 million years ago that allowed our ancestors (and the ancestors of chimpanzees and gorillas) to have the remarkably enhanced ability to metabolize ethanol. As Carrigan said, just in this same period, our planet started cooling off, sources for food had changed, and thus this primate ancestor began to explore life on the ground.

The ability to metabolize ethanol did happen quite long before human-directed fermentation, and it was possibly useful for primates who had lived at the places in which a large amount of highly fermented fruit was handy, especially at times when there was a shortage of food. As fruit taken from the ground had higher concentrations of fermenting yeast and ethanol compared with the same fruits hanging on trees, it should be the transition for the first time that our ancestors were exposed to sufficient amounts of dietary ethanol.

According to Carrigan, supposing that you were the ancestor without this new mutation in ADH4, the ethanol would be rapidly accumulated in your blood and you would be inebriated more quickly. Getting sick or drunk off fruit would make you unable to guard your territory or go looking for food; therefore, selection should do favor to those with the new mutation.

In addition, these new discoveries may give clues to the reason why our brains have evolved to associate pleasure pathways with alcohol consumption, because ethanol was closely linked with a key food source.

Image source: Reza via Flickr CC BY 2.0

Journal reference: Carrigan, Matthew A., et al. “Hominids adapted to metabolize ethanol long before human-directed fermentation.” Proceedings of the National Academy of Sciences (2014): 201404167.