Some chimps in Guinea seem to have developed a taste for alcohol and at times have even appeared to be drunk, according to a 17-year study of the primates that lends support to the "drunken monkey hypothesis."
In the study published in the journal Royal Society of Open Science, researchers said they discovered chimpanzees raiding buckets of sap from raffia palm trees being collected by local residents to make their own alcohol,
according to the BBC News. The sap creates a naturally fermented palm wine.
The chimpanzees were observed numerous times creating leaf sponges – handfuls of leaves that they chew and crush into an absorbent mass – to dip into the sap and then suck out the contents. Researchers said some chimps would use big leaves as a scoop to get the sap out of the container,
according to The Guardian.
"Chimpanzees ingest fermented palm sap at Bossou rarely, but habitually," said the
Royal Society study. "… The behavior is consistent with some degree of social transmission. All age and sex classes ingested palm sap, and there was no sex bias in the quantity of ethanol ingested during a feeding event."
"In addition, there does not appear to be a pattern in the amounts ingested by the same individual in different events. Some of the chimpanzees at Bossou consumed significant quantities of ethanol and displayed behavioral signs of inebriation. Researchers rarely collected detailed behavioral data before versus after exposure to ethanol, but some drinkers rested directly after imbibing fermented sap," said the study.
The Guardian said Kimberley Hockings, the lead author of the study at Oxford Brookes University, stated that while researchers did not know definitively that the chimpanzees were actually drunk, they could tell the animals consumed enough sap during their drinking sessions that it could "elicit behavioral changes in humans."
Researchers observed that after one such session one adult male chimp appeared restless while his drinking buddies spent the next hour swinging from tree to tree "in an agitated manner."
The Royal Society researchers said the study seemed to support the "drunken monkey hypothesis" that theorizes that natural selection favors primates with a taste for alcohol because it stimulates the appetite and helps the species hunt for fruit to increase calorific intake.
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