Chimpanzees would fail a breathalyser test because they consume fruit containing alcohol, a study has found.
Researchers discovered that the fruits that chimpanzees eat in the wild contain sufficient alcohol to provide around 14 grams per day, equivalent to around two standard drinks.
UC Berkley Phd student Aleksey Maro and adviser Robert Dudley, the university’s professor of integrative biology, used new urine sampling techniques during a collecting trip to Ngogo in Uganda’s Kibale National Park.
Mr Maro was able to confirm that chimpanzees naturally ingest alcohol in their diet, and even seek it out.
Working alongside Sharifah Namaganda, a Ugandan graduate student at the University of Michigan, Maro gathered forked branches and covered the ends with plastic bags to create effective bowls collecting samples from chimpanzee urine.
He then waited under trees where chimps were feeding and waited for signs of movement – as the apes tend to urinate before leaving a feeding spot.
The results, published in the journal Biology letters, show that the urine of most chimpanzees sampled contained a metabolic byproduct of alcohol called ethyl glucuronide. This, researchers said, proved they ingest significant quantities of ethanol in their diet, likely coming from the fermenting fruits.
“We find widespread physiological evidence of the consumption of alcohol by chimpanzees,” Maro said. “If there’s any doubt about the drunken monkey hypothesis—that there’s enough alcohol in the environment for animals to experience alcohol in a way analogous to humans—it’s been cleared up.”
Out of 20 urine samples from 19 chimpanzees, 17 contained 300 nanograms per milliliter (ng/ml) or more of ethanol, while 10 contained 500ng/ml.
A level of around 500ng/ml is typical in humans after light drinking, such as one to two drinks, within the previous 24 hours.
A possible consequence of these results is that, as descendants of fruit-eating apes, humans likely evolved the same tendency to seek out alcohol for their diet.
“The levels are high, and this is a conservative estimate given the time course of exposure throughout the day,” Dudley said. “In nanograms per milliliter, these are coming in way above some of the clinically relevant and forensically relevant human thresholds.”
He said the result “corroborates the inferred ingestion rates that Aleksey derived previously”.
Mr Maro had previously collected samples of the types of fruit chimpanzees are known to eat, before measuring the ethanol concentration in the fruit pulp and estimating how much alcohol the average chimp would consume.
The next step for the researchers is to “definitively prove the universal hypothesis of attraction to alcohol”.
