Behind every sip of beer you drink, there are millions of years of evolution at work. Research into 70 million years of primate evolution indicates that our ancestors evolved a markedly enhanced ability to metabolize or break down ethanol 10 million years ago. Who knew they had happy hours back then?

That doesn't mean that humans have been drinking wine and beer that long. After the first civilizations formed in the Middle East about 9,000 years ago, people discovered that the fermentation process preserves food. That is probably when people began experimenting with alcoholic beverages. Previously, historians believed this was the first time alcohol, that is specifically ethanol, entered the human diet. It has been argued that alcoholism is due to the relatively short amount of time humans have been consuming ethanol, which has not allowed us evolve an effective way of metabolizing and digesting it.

However, the new theory suggests that early primates began eating low amounts of ethanol around 80 million years ago when flowering plants began producing fruit. These fruits became infected with yeast that was capable of fermenting the sugars stored within. Then, as primates began living on the ground below instead of in the trees, they would have eaten the fruit that fell to the ground, which would have been at various stages of fermentation with even higher levels of ethanol. This would have given them an evolutionary advantage over other species that could not break down ethanol.

When we digest ethanol, it is absorbed in the small intestine, enters the blood stream, moves to the liver and is metabolized there by enzymes called alcohol dehydrogenase, or ADH and aldehyde dehydrogenase. These enzymes work together to break down ethanol molecules to carbon dioxide and water. In this process, ethanol is first converted to acetaldehyde, a very toxic and highly reactive molecule. Some acetaldehyde enters your blood, causing tissue damage. We can thank acetaldehyde for our hangovers and their symptoms.

A small amount of alcohol is also excreted through sweat, saliva, urine and your breath, which is how it can be detected by a breathalyzer test. Since alcohol is metabolized more slowly than it is absorbed, drinking too much too quickly causes alcohol to accumulate in the body, resulting in intoxication.

To determine when our ancestors developed the ability to metabolize ethanol, scientists looked for a version of ADH in primates along our evolutionary tree. They looked for when there was a molecular change in the gene encoding the enzyme that made it more active against ethanol. Of the 19 primates that evolved in the past 70 million years, only hominids and four other primates have the enzyme. This group split off 13-20 million years ago, which corresponds to our enhanced ability to enjoy ethanol. Even today, primates with this enzyme can eat lower quality, partially fermented foods, unlike other primates.

We have our ancestors to blame for our attraction to alcohol. It turns out our kind has been partying for much longer than previously thought.

Medical Discovery News is hosted by professors Norbert Herzog at Quinnipiac University, and David Niesel of the University of Texas Medical Branch. Learn more at www.medicaldiscoverynews.com.