Humans and their ancestors have been consuming ethanol in its most basic form for nearly 10 million years, according a study published Monday by PNAS (Proceeding of the National Academy of Science). Ethanol is the kind of alcohol in liquor and fuel but is also found in rotting fruit—and fruit was the primary food of our hominid ancestors.
Santa Fe College biology professor Matthew Carrigan led a team of researchers at the Foundation for Applied Molecular Evolution who studied our primate ancestors to determine when humans gained the ability to metabolize ethanol. His study “Hominids Adapted to Metabolize Ethanol Long Before Human-directed Fermentation” finds that an enzyme in our primate ancestors evolved the ability to metabolize ethanol significantly earlier the 9,000-year timeframe that has long been theorized.
“Many aspects about the modern human condition—everything from back pain to heath issues caused by ingesting too much salt, sugar and fat—is related to our evolutionary history,” Carrigan said. “By understanding ‘if’ and ‘when’ our human ancestors adapted to ethanol, we hope to better understand ‘why’ humans sometimes consume unhealthy amounts of ethanol.”
The research team examined an enzyme known as Class IV alcohol dehydrogenases (ADH4) found in the mouth and stomach of primates that humans diverged from 70 million years ago. They studied the genetic sequences of 17 primates, synthesizing nine different ancient ADH4 proteins to determine how past versions of the enzyme worked. They tested each one for their ethanol-metabolizing properties.
The team discovered that ADH4 enzymes from ancient primates were not able to metabolize ethanol. This changed dramatically about 10 million years ago when the common ancestor of humans and gorillas began adapting to life on the ground. At that point, a single amino-acid alteration in the enzyme made ADH4 40 times more effective at breaking down ethanol.
As this common ancestor of humans and gorillas adapted to life on the ground, they likely encountered fallen fruit that had begun to ferment naturally. Those that could eat the fermenting fruit without getting inebriated may have had a better chance of surviving, particularly during periods of food scarcity. While fermented fruit may not have been an optimal food source, it appears the ancestors benefitted from the ability to consume it.
This research on our human ancestry has implications not only for understanding the forces that shaped early human terrestrial adaptations but also for many modern human diseases caused by alcohol today. This research was funded by a grant from the National Institute on Alcohol Abuse and Alcoholism to Thomas Hurley and Steven Benner.