Drunken monkeys and the 10mn year-old origins of alcohol consumption
The consumption of alcohol is something we take for granted, but the ability to consume ethanol may in fact have played an important part in primate evolution, a new study published in the Proceedings of the National Academy of Sciences suggests. Liking a drink is not just a modern quirk, since our ancestors are thought to have benefited from consuming alcohol as long as ten million years ago – something to mull over with your next glass of wine!
The fermentation of fruits with honey is thought to be the first evidence of human contact with alcohol 9000 years ago; however, our association with this intoxicating substance is thought to have a far older source. The ‘drunken monkey hypothesis’ suggests that the ability to consume moderate amounts of alcohol evolved in our ancestors many millions of years ago, as a result of the benefits of being able to eat fruit that had fallen from the tree. Ripe, fallen fruit contains high levels of fermenting sugars and a correspondingly high level of ethanol that would have been toxic to animals unable to metabolize it efficiently. Meanwhile, individuals with improved alcohol metabolism would have avoided ill-effects and retained a selective advantage over their lightweight contemporaries.
The breakdown of alcohol in humans and other primates is facilitated primarily by the enzyme alcohol dehydrogenase 4 (ADH4). Its efficiency varies between species, and most primate ancestors would have been unable to metabolize more than a small quantity of alcohol. However, a new study led by Matthew Carrigan at Santa Fe College has suggested that 10 million years ago a common ancestor of humans, chimps and gorillas evolved a version of ADH4 that was 40 times more efficient than earlier forms of the enzyme. The research group sequenced the ADH4 gene from 19 modern primate species, mapped the gene variants to different points in primate history and investigated the metabolism potential of the resultant proteins to generate their conclusions.
The results suggest that the 10 million year-old boost in ADH4 might have had behavioural consequences, and even contributed to a more terrestrial lifestyle among many higher primates. Carrigan even proposes that the evolutionary pathway of ethanol tolerance could explain our partiality for a beverage. Alcohol consumption is linked to pleasure pathways in the brain – could this be due to the evolutionary importance of ethanol as a food source?
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