Wild Chimpanzees Consume Alcohol from Fermented Fruit, Offering Insights into Human Attraction to Alcohol

A study published in Biology Letters reports that wild African chimpanzees consume alcohol by eating fermented fruit, an observation that may offer insights into the evolutionary origins of human attraction to alcohol.

Researchers analyzed urine samples from chimpanzees in Uganda, detecting ethanol in a significant number.

Key Study Findings

The research, led by Aleksey Maro, a Ph.D. student at UC Berkeley, involved collecting and analyzing chimpanzee urine samples from the Ugandan rainforest.
Out of 19 chimpanzees tested, 17 showed positive results for ethanol.
At least 10 of these samples contained alcohol concentrations equivalent to one to two standard human drinks.

Chimpanzees consume an average of 10 pounds of fruit pulp daily, including fruits such as the African star apple. When these fruits ripen, they can ferment and produce alcohol.
Researchers state that primates are not believed to consume enough alcohol through these natural sources to become intoxicated.

Methodology

Field collection of urine samples was conducted by Maro and Sharifah Namaganda, a Ph.D. candidate at the University of Michigan, who assisted in the field.
Methods included using plastic bags to catch droplets from overhead chimpanzees and pipetting samples from leaves.
Samples were typically collected in the morning and immediately tested for metabolized alcohol, with an emphasis on ensuring minimal contamination.

Maro had previously demonstrated that many ripe fruits in the chimpanzee diet in regions including Uganda and Côte d'Ivoire contain ethanol.

Potential Implications

The study suggests that the smell of alcohol might signal the presence of sugars, potentially serving as a shortcut for primates to obtain more calories. This association with a sugary reward is hypothesized to explain the evolutionary origin of human attraction to alcohol.

Maro described the findings as "tantalizing," noting that while the sample size is small, alcohol may have been a natural component of ancestral primate diets.

This historical exposure might contribute to modern human attraction to alcohol, particularly given the ability to concentrate it today.
Sharifah Namaganda highlighted that great apes provide valuable insights into human evolutionary behavior, including the origins of alcohol preference. The affinity for fermented substances has also been observed in other species, such as fruit flies.

Expert Perspectives

Primatologist Cat Hobaiter, who was not involved in the study, commented that these findings could open new avenues for understanding chimpanzee behavior and the evolutionary origins of human cultural and social rituals involving alcohol.
Matthew Carrigan, an evolutionary biologist not involved in the research, characterized the study as "wonderful," stating it supports previous research through direct measurement of alcohol metabolism.

Future Research

A subsequent research step will involve determining whether chimpanzees actively exhibit a preference for fruits containing alcohol or consume them incidentally.