It would appear alcohol consumption has been a part of human life longer than previously thought. According to a study, humans may have developed a liking for alcohol around 10 million years ago, way before modern humans created their own brews.

Published in the journal Proceedings of the National Academy of Sciences, the study sought to better understand modern human condition in terms of alcohol consumption, saying that many aspects of today's life have evolutionary history. There have been many attempts before to answer the question of when humans started consuming alcohol-containing food but theories have wildly varied.

One theory supposes that primates consumed ethanol regularly about 80 million years ago when they picked up fleshy fruits on the ground which started to ferment some time after dropping.

To narrow down the timeline to something more specific, researchers focused on the genetic evolution of an enzyme called ADH4. The enzyme had been present in primates in various forms for at least 70 million years now and is the first to encounter ethanol after it is consumed.

With the help of genetic sequences from 28 mammals (17 of which were primates), researchers worked backwards to create a family tree of sorts for ADH4. To determine how past versions of the enzyme worked, researchers synthesized nine different ADH4 proteins, testing each one for their ethanol-metabolizing properties.

Almost all of the ADH4s from primates were not able to metabolize ethanol but about 10 million years ago, around the point when humans and orangutans diverged, something dramatic happened. This led to a single amino-acid alteration in the enzyme, rendering ADH4 40 times more effective at breaking down ethanol than before.

The evolved ADH4 came around a time that the ability to digest alcohol would be useful, like when human ancestors turned to ground-level sources of food. Environmental changes could have pressured earlier primates to transition from forest ecosystems to grasslands.

Lead author Matthew Carrigan, a paleogeneticist from Santa Fe College, however, suspects human ancestors weren't too fond of ethanol, despite developing the ability to metabolize it.

"If the ancestors of humans, chimps and gorillas had a choice between rotten and normal fruit, they would go for the normal fruit. Just because they were adapted to be able to ingest it doesn't mean ethanol was their first choice, nor that they were perfectly adapted to metabolize it. They might have benefited from small quantities, but not to excessive consumption," he explained.

Other authors for the study include: Oleg Uryasev, Carole Frye, Blair Eckman, Candace Myers, Thomas Hurley and Steven Benner.