Researchers were hoping to shed light on when, exactly, human ancestors acquired the ability to consume foods containing ethanol, such as fermented fruits. Attempts to answer this question have yielded wildly divergent theories. One theory holds that primates regularly ingested ethanol some 80 million years ago as plants started producing fleshy fruits that could drop and ferment on the ground. Other scientists believe humans started enjoying ethanol just 9,000 years ago when we learned how to ferment foodstuffs.
To help narrow that range, researchers studied the genetic evolution of alcohol-metabolizing enzyme ADH4, which has been present in primates, in one form or another, for at least 70 million years. Using genetic sequences from 28 different mammals, including 17 primates, the researchers were able to work backward and create a sort of family tree for ADH4.
To see how the past versions would have worked, researchers then synthesized nine different ADH4 proteins and tested their ethanol-busting properties.
Nearly all of the ADH4 enzymes from our primate ancestors were inactive — meaning they didn’t break down ethanol. However, about 10 million years ago, when orangutans and human ancestors diverged, things changed dramatically. A single amino acid alteration made ADH4 able to metabolize ethanol 40 times better than before.
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