Happy hour started way earlier than we thought.

Roughly 10 million years ago - long before humans began to store food harvested by agriculture, and long, long before they intentionally fermented food and made a delightfully relaxing ritual of consuming the result - a new study finds that the guts of our primate ancestors evolved the ability to metabolize alcohol.

The latest research suggests that humankind has had far more evolutionary time to adapt itself to the presence of alcohol than has been previously thought. Earlier efforts to date mankind's practice of consuming alcohol had suggested that our relationship to fermented fruit began a mere 9,000 years ago. That is when humans were thought to have developed the technological wherewithal to jump-start the rotting process, separate the extraneous food bulk, and harvest the liquid inebriate known by the scientific name of ethanol.

If humankind's relationship with drink were truly that young, it would stand to reason that many among us might not yet have acquired the evolutionary means to tolerate alcohol. And that would likely color our understanding of a disease such as alcoholism - in which an environmental factor that is benign or even salutary to most confers toxic effects on certain individuals. Alcoholics might be seen merely as evolutionary late bloomers, whose genetic ability to metabolize ethanol has not yet caught up with its availability.

If primates have been enjoying the effects of fermentation for 10 million years, by contrast, that would suggest that humans - and even chimpanzees and gorillas before them - have by now pretty fully evolved to consume alcohol. By that reading, any genetic predisposition to alcoholism might be viewed as the result of a more recent, or more random, genetic mutation.

A team led by biologist Matthew Carrigan of Santa Fe College in Gainesville, Fla., reached back into humans' ancestral lineage to detect where the ability to produce a gut enzyme key to metabolizing alcohol appeared. Their research was published Monday in the journal PNAS.