Chimpanzees in the wild have not only discovered nature-produced palm wine, but they have also developed various leafy tools for tippling.
A new study suggests that the last common ancestor of living African apes and modern humans was not averse to imbibing - and otherwise ingesting - foods and liquids containing alcohol.
The findings, published in the journal Royal Society Open Science, reveals the intelligence of our closest living primate relatives.
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"Chimpanzees at Bossou (Guinea, West Africa) have applied their knowledge of how to make and use leafy tools to exploit a new liquid resource, palm wine," lead author Kimberley Jane Hockings of Portugal's Center for Research in Anthropology and Oxford Brookes University told Discovery News.
She added, "This new use of elementary technology shows once again how clever and enterprising are humankind's nearest living relatives."
Hockings and her team followed up on anecdotal reports of Bossou villagers who observed chimpanzees - often male chimps in groups - drinking palm wine and appearing drunk afterwards. The apparently happy ritual probably spread via social transmission from chimp to chimp.
It began after locals set out containers to collect the fermented, alcohol-rich dripping sap from raffia palm trees. Chimps found the containers, and adapted tools that they normally use to drink water to gulp down the natural brew, which has nearly as much alcohol as common grape wines.
The chimpanzees first make the tools by either folding leaves into a cup shape or crumbling them up in their mouths into more of a sponge-like object.
"This absorbent, extractive tool is dipped into the opening of the fermented palm sap container, then retrieved and put into the mouth for drinking," Hockings explained.
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As for how an inebriated chimp acts, the effects of alcohol consumption appear to be just as varied as they are for humans. Hockings said that she saw one chimp sleeping off his liquid lunch. Another, however, became hyperactive, "moving from tree to tree in an agitated manner" long after his fellow chimps had settled into their night nests.
While male and female, as well as young and old, chimps were seen drinking the palm wine, males accounted for 34 of the 51 documented events.
It is not possible yet to tell if the chimps are attracted to palm wine as a food source, or if they like the feeling of being intoxicated, which may fuel their consumption. It could be that these two possibilities are not mutually exclusive, since the wine does contain some nutrients.
The study cites research led by Matthew Carrigan, an assistant professor of biology at Santa Fe College. Carrigan and his team believe that around 10 million years ago, the last common ancestor of humans and living African apes evolved an enhanced ability to metabolize ethanol (alcohol). Interestingly, orangutans in Asia do not share this 40-fold ability to process alcohol.
The researchers suspect that a more terrestrial lifestyle among African primates increased the possibility of encountering fermenting fruits on the ground. These fruits might have been heavily consumed during certain times of the year when fresh fruits were scarce and other resources were limited.
Carrigan told Discovery News that the new findings "demonstrate that wild chimpanzees are not averse to ethanol, (and) that chimpanzees do not avoid food containing ethanol, even when these concentrations are sufficiently high as to be easily detected and capable of producing physiological effects."
He said that the study opens up many new questions, such as how widespread among other primates is the willingness to consume alcohol? What factors might preclude a primate deciding to go after this food source? Do non-human primates merely tolerate alcohol's presence in otherwise nutritious drinks/foods, or do they truly enjoy it and seek it out?
"There are many unanswered questions," Carrigan said, adding that the new determinations "provide an important step towards understanding the evolution of a human behavior that is of great social consequence."