Drunken Apes In West Africa Could Explain Our Love For Alcohol

Chimpanzees have been known to indulge in uncannily human-like behavior, from the ability to laugh out loud, to having a basic understanding of human language. Scientists are now discovering that these aren’t the only areas where our closest living relatives resemble humans.

Chimpanzees and humans, it turns out, share a taste for alcohol. And, according to a new study, many of our primate cousins are habitual drinkers who enjoy naturally fermented palm wine, produced by raffia palm trees. In addition to confirming that chimps do in fact love a tipple as much as humans do, and that they do occasionally go over the top -- again, much like humans do -- the new study also provides evidence for the so-called “drunken monkey hypothesis.”

“Some individuals were estimated to have consumed about 85ml of alcohol and displayed behavioral signs of inebriation, including falling asleep shortly after drinking,” Kimberley Hockings from Oxford Brookes University in the U.K. and the Centre for Research in Anthropology in Portugal, who led a research team studying chimpanzees in a colony at Bossou in southern Guinea, said, in a statement released Wednesday.

These chimps were observed using drinking tools called leaf sponges -- created using handfuls of leaves that they chew and crush into absorbent sponges -- to dip into the fermented palm sap and suck out the contents.

“Over 17 years, we observed 51 fermented palm sap drinking events recorded during 20 drinking sessions involving 13 adult and immature individuals,” the researchers said, in a study published in the journal Royal Society Open Science. “Thirteen of 26 adult and immature individuals present in the Bossou community between 1995 and 2012 (excluding infants) were never seen ingesting palm sap.”

On several occasions, these chimps also organized group drinking sessions, passing around the leaf sponges to their buddies.

Although villagers in the region have reported seeing these chimps sampling the palm sap left out in containers to ferment, this is the first time scientists have recorded and measured voluntary -- and habitual -- alcohol consumption in any wild ape.

The drunken monkey hypothesis, which is an attempt to explain humans' predilection for alcohol, states that this attraction could have provided an evolutionary advantage to our ancestors. It posits that the genetic ability to break down alcohol could have allowed our ancestors to digest overripe and fermenting fruit -- giving them a survival advantage over those who couldn’t.

The latest study shows that this ability was handed down not only to humans, but also to chimpanzees, which split from the human line about six million years ago.

“Further palaeogenetic and ethological research may offer insight into potential subspecies and interpopulation differences in chimpanzees’ ability to oxidize ethanol,” the researchers said, in the study. “Examination of these factors should allow further specific testing of the ‘drunken monkey hypothesis.’”