It is believed that man had his first taste of alcohol 9,000 years ago when Chinese villagers fermented fruit and honey to brew an intoxicating drink, but researchers have found evidence that long before humans started to booze, our human ancestors had already evolved the ability to consume alcohol.

For a new study published in the Proceedings of the National Academy of Sciences on Dec. 1, researchers studied the genetic evolution associated with the alcohol-metabolizing enzyme called ADH4 over the last 70 million years.

Matthew Carrigan from the Department of Natural Sciences at Santa Fe College, together with colleagues, sequenced the genomes of 28 different mammals, 17 of which were primates, to know how the ADH4 genes evolved and what these genes might have looked like in the ancestors of the animals. The researchers also tested how these past versions of ADH4 work in breaking down ethanol.

Carrigan and colleagues found that almost all of the primitive ADH4 enzymes could not break down alcohol. About 10 million years ago, however, when the orangutans and human ancestors diverged, a single genetic mutation occurred that gave our human ancestors the ability to consume and break down ethanol.

The researchers said that the timing of the mutation also occurred when our human ancestors shifted to a terrestrial lifestyle. The ability to break down alcohol appears to have provided an advantage as this allowed our human ancestors to dine on rotting and fermenting fruit particularly when food was scarce.

"Exposure to dietary sources of ethanol increased in hominids during the early stages of our adaptation to a terrestrial lifestyle," the researchers wrote. "Because fruit collected from the forest floor is expected to contain higher concentrations of fermenting yeast and ethanol than similar fruits hanging on trees, this transition may also be the first time our ancestors were exposed to (and adapted to) substantial amounts of dietary ethanol."

Carrigan said that although our ancestors were able to ingest alcohol, it does not mean that they were fully adapted to metabolize it. They may have benefited from consuming small quantities of ethanol but not to excessive amounts.

In present-day humans, drinking in moderation is associated with some benefits but consuming too much alcohol is linked with health problems. Scientists said that the diseases and maladies associated with too much drinking are the result of humans not having evolved the genes to process ethanol sufficiently.

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