Posts Tagged ‘chimpanzees’

Boozy chimps, Hanuman and the “drunken monkey” hypothesis

June 11, 2015

A new paper reports on chimpanzees in Guinea exhibiting long-term and recurrent ingestion of ethanol. The study was carried out over 17 years and found chimpanzees using leaves to drink fermented palm sap. Many consumed sufficient to produce “visible signs of inebriation”. Local humans also tap the sap of the raffia palm trees to make a palm wine.

The human trait of imbibing intentionally fermented drinks is at least as old as the oldest known archaeological records of ancient civilizations. Stone jugs for alcoholic drinks have been found which date back to at least 10,000 BCE . It is quite likely that the origin of alcoholic drinks predates the arrival of agriculture some 15,000 years ago. And that would suggest that the origin lies with the accidental (and fortuitous?) consumption of over-ripe and partially fermented fruits and berries leading eventually to an intentional fermentation. But that takes the origin back to the time before modern humans had even arrived on the scene and when their primate ancestors relied on fruits and berries for their diet.

Kimberly J Hockings, et al, Tools to tipple: ethanol ingestion by wild chimpanzees using leaf-sponges, Royal Society of Open Science

AbstractAfrican apes and humans share a genetic mutation that enables them to effectively metabolize ethanol. However, voluntary ethanol consumption in this evolutionary radiation is documented only in modern humans. Here, we report evidence of the long-term and recurrent ingestion of ethanol from the raffia palm (Raphia hookeri, Arecaceae) by wild chimpanzees (Pan troglodytes verus) at Bossou in Guinea, West Africa, from 1995 to 2012. Chimpanzees at Bossou ingest this alcoholic beverage, often in large quantities, despite an average presence of ethanol of 3.1% alcohol by volume (ABV) and up to 6.9% ABV. Local people tap raffia palms and the sap collects in plastic containers, and chimpanzees use elementary technology—a leafy tool—to obtain this fermenting sap. These data show that ethanol does not act as a deterrent to feeding in this community of wild apes, supporting the idea that the last common ancestor of living African apes and modern humans was not averse to ingesting foods containing ethanol.

The study provides support for the “drunken monkey” hypothesis which “proposes that human attraction to ethanol may derive from dependence of the primate ancestors of Homo sapiens on ripe and fermenting fruit as a dominant food source. Ethanol naturally occurs in ripe and overripe fruit when yeasts ferment sugars, and consequently early primates (and many other fruit-eating animals) have evolved a genetically based behavioral attraction to the molecule”.

In fact there were natural selection benefits in being “drunken monkeys”. The chimpanzee paper begins:

The ‘drunken monkey hypothesis’ states that natural selection favoured those primates with an attraction to ethanol (commonly referred to as alcohol) because it was associated with proximate benefits (e.g. acting as an appetite stimulant or a cue to finding fruit, or as an unavoidable consequence of a frugivorous diet, etc.), consequently increasing caloric gains.

Hanuman chasing the Sun — image Wikipedia

It is a short mental step from monkey-ancestors to ancient civilizations and mythology. The Indian monkey-god, Hanuman was supposed to be both celibate and teetotal. But his depiction as a “monkey” is probably a later invention. Ancient texts suggest that the young Hanuman was so enamoured of red fruit that he tried to eat the Sun, thinking it was just another ripe fruit. Quite possibly his red fruit were over-ripe, partially fermented and intoxicating. The resulting disfigurement to his jaw and face (burnt and swollen) is what may have given him his appearance. There is a hint that he was of an ancient people (species), half-human and half-monkey, which has become extinct. An ancient ancestor perhaps, and one addicted to intoxicating fruit. Clearly he was put off alcohol for ever. Interestingly, mythology and ancient ayurvedic medicine agree that alcohol in moderation is medicinal and good but taken in excess is a poison and bad. Of course in the Ramayana, all the good guys are vegetarians and teetotal while all the bad guys eat meat and consume an excess of alcohol. The Mahabharata is much more equivocal. Here even the good guys are allowed to drink.

Chimpanzees and orangutans have long term memories too

July 19, 2013

image The Telegraph

Interesting work in a new paper is published in Current Biology. It supports my view that life is a continuum from simple to complex with no place for – or any need to invoke – a “soul”. At what point the brain of a species is large enough and complex enough not only to be able to “save” memories but also to then access these data at a later time is also unknown. I have little doubt from the  dogs and cats that I have known that they can “remember” people and behaviour from many years before  – even if they are often  supposed to live only in the “now”. At what point in this continuum “self-awareness” emerges is not known but I suspect that it depends on the definition of “self-awareness” and some level of self-awareness lies very close to the “simple” end of the scale of life.

(Certainly the mosquito which got trapped in my study yesterday was not just “self-aware”, it was also maliciously aware of me. If it had a soul it has now been consigned to mosquito hell!!)

This work shows that chimpanzees and orangutans have the ability to “remember events that happened two weeks or three years ago, but also that they can remember them even when they are not expecting to have to recall those events at a later time” 

Gema Martin-Ordas, Dorthe Berntsen, Josep Call. Memory for Distant Past Events in Chimpanzees and OrangutansCurrent Biology, 2013; DOI: 10.1016/j.cub.2013.06.017


  • First study addressing unexpected and cued recall of both general and unique events
  • Chimpanzees and orangutans recalled events that happened weeks and years earlier
  • Subjects also showed evidence of binding
  • Chimpanzees and orangutans share this form of autobiographical memory with humans


Determining the memory systems that support nonhuman animals’ capacity to remember distant past events is currently the focus an intense research effort and a lively debate. Comparative psychology has largely adopted Tulving’s framework by focusing on whether animals remember what-where-when something happened (i.e., episodic-like memory). However, apes have also been reported to recall other episodic components after single-trial exposures. Using a new experimental paradigm we show that chimpanzees and orangutans recalled a tool-finding event that happened four times 3 years earlier (experiment 1) and a tool-finding unique event that happened once 2 weeks earlier (experiment 2). Subjects were able to distinguish these events from other tool-finding events, which indicates binding of relevant temporal-spatial components. Like in human involuntary autobiographical memory, a cued, associative retrieval process triggered apes’ memories: when presented with a particular setup, subjects instantaneously remembered not only where to search for the tools (experiment 1), but also the location of the tool seen only once (experiment 2). The complex nature of the events retrieved, the unexpected and fast retrieval, the long retention intervals involved, and the detection of binding strongly suggest that chimpanzees and orangutans’ memories for past events mirror some of the features of human autobiographical memory.

From Science Daily:

…. “Our data and other emerging evidence keep challenging the idea of non-human animals being stuck in time,” says Gema Martin-Ordas of Aarhus University in Denmark. “We show not only that chimpanzees and orangutans remember events that happened two weeks or three years ago, but also that they can remember them even when they are not expecting to have to recall those events at a later time.” ….. 

“I was surprised to find out not only that they remembered the event that took place three years ago, but also that they did it so fast!” Martin-Ordas says. “On average it took them five seconds to go and find the tools. Again this is very telling because it shows that they were not just walking around the rooms and suddenly saw the boxes and searched for the tools inside them. More probably, it was the recalled event that enabled them to find the tools directly.”

%d bloggers like this: