New research suggests humans and their ancestors have had a taste for an occasional stiff drink for as long as 10 million years,
The findings could provide insight into the lifestyles of our primate ancestors and even help researchers gain a better understanding of alcoholism and why it occurs, Science AAAS reported. In the past, scientists had suggested humans most likely developed their love for alcohol about 9,000 years ago, when people started fermenting food-- these new findings suggest otherwise.
Metabolizing ethanol (the ingredient in alcohol that causes drunkenness) without getting sick requires a set of proteins including alcohol dehydrogenase enzyme ADH4. All primates possess ADH4, which breaks down ethanol, but this does not necessarily mean they have the tools to metabolize it. Primates such as lemurs and baboons have a version of ADH4 that is much less effective than what is possessed by humans.
To make their findings the researchers sequenced ADH4 proteins from 19 modern primates and worked backwards to determine how its efficiency changed throughout history. The team also created copies of some of these ancient proteins to determine how well they metabolized ethanol. The analysis revealed ADH4 found in primates 50 million years ago was not very efficient at metabolizing ethanol, but about 10 million years ago human ancestors developed a version that was about 40 times more powerful.
"Around this same time, the Earth cooled off, food sources changed, and this primate ancestor started to explore life on the ground," Matthew Carrigan, a biologist at Santa Fe College, told Science AAS.
At around this point in history human ancestors started to munch fruit that had fallen from trees, many of which had already been exposed to bacteria which started to converting sugars into alcohols. Without the new gene mutation these early hominids most likely got drunk off the fruit quicker than a modern human would.
"If you were the ancestor without this new mutation in ADH4, the ethanol would quickly build up in your blood and you'd get inebriated much faster," Carrigan said. "You'd be a cheap date."
The mutation most likely developed for survival purposes, because primates that were tipsy were not as efficient at defending their territory. Primates with this mutation would also have the ability to get more food. The findings could help shed light on why the modern human brain associates alcohol with pleasure, sometimes leading to debilitating addictions.
"It's not a whole lot different from the addictions some people have towards food," Carrigan said. "At the right dose, when you didn't have alcohol and candy at every corner, it was hard to get too much of this sort of stuff, so when you found it, you wanted to be programmed to overconsume."
The findings were published in a recent edition of the journal the Proceedings of the National Academy of Sciences.
