IT’S the longest period of abstinence on record. Vertebrates gained the genes used to metabolise ethanol 310 million years before flowering plants started producing significant amounts of the intoxicating stuff.

The gene for alcohol dehydrogenase (ADH) – a protein that breaks down ethanol – was originally thought to have evolved in humans in response to the creation of liquor. But then the enzyme was discovered in animals, so it was thought that the protein emerged to break down ethanol in the fermenting fruit of flowering plants. These appeared on Earth around 140 million years ago.

Now Héctor Riveros-Rosas at the National Autonomous University of Mexico in Mexico City thinks it is time to change the story again. He analysed the available ADH gene sequences from animals, and says they suggest that ADH first appeared in vertebrates some 450 million years ago – long before flowering plants evolved, and even before the conifers that appeared around 315 million years ago began producing sweet berries that can ferment to generate small quantities of alcohol.

Riveros-Rosas believes ADH was initially used to metabolise natural hormones, and was later hijacked for our bacchanalian pleasures. He points out that studies have found evidence that ADH breaks down naturally produced hormones such as dopamine much faster than ethanol.

However, the new study does suggest that some animals evolved a version of ADH in response to the appearance of fruit. Fruit flies gained the gene between 70 and 135 million years ago (Chemico-Biological Interactions, DOI: 10.1016/j.cbi.2011.02.008).