'Drunk Monkey' Theory Supported by Tippling Chimps

Chimpanzees appear to enjoy drinking alcohol-containing palm sap. In this photo, chimpanzee Yangyang (left, who was born in Guinea) kisses his "bride" Wanxing during their symbolic wedding at Hefei Wildlife Park in Hefei, China. Reuters

Humans are not the only animals that consume alcohol and occasionally become intoxicated. Various types of birds like Bohemian waxwings have been known eat fermented berries, occasionally so much so that they can't fly. Malaysian tree shrews apparently have a taste for fermented palm nectar. Green monkeys on the Caribbean island of St. Kitts have been known to nab tourists' cocktails.

Now, research shows that chimpanzees in West Africa seem to enjoy drinking fermented palm sap, also known as palm wine, sometimes to the point of visible intoxication.

In a study published June 9 in the journal Royal Society Open Science, researchers recorded the number of times that chimpanzees drank alcohol-containing sap outside Bossou, a town in southeastern Guinea, from 1995 to 2012. They found that during this time, 13 different chimps tippled on the sap, drinking it in groups or alone, and often in large quantities. The sugary sap oozes out after local humans tap the trees, and quickly ferments, collecting in plastic containers people leave there. The scientists found this liquid contains between three and nearly seven percent alcohol, equivalent to the levels of ethanol in beer.

The results support the "drunken monkey hypothesis," which "states that natural selection favored those primates with an attraction to ethanol," the study notes. Alcohol is present in ripe, nutritious fruits that ferment—so being able to stomach it and break it down would be a beneficial adaptation. Chimpanzees, humans and many other primates can metabolize ethanol, an adaptation that probably traces to a common ancestor tracing back perhaps 10 million years. Many non-primates appear to lack this ability and are easily poisoned by alcohol.

With that in mind, let us all watch a video of monkeys stealing drinks (and getting plastered) in St. Kitts.