Chimpanzee social bonding may involve food as well as grooming. A 2025 field study reports that wild chimpanzees eat fruit containing small amounts of naturally produced ethanol and, in some cases, share it. For Paper I it is a memorable case of primate diet, food sharing and the evolutionary background of human commensality. Frame it around sharing, not around drinking.
Source: Anna Bowland et al., Current Biology (21 April 2025); fieldwork in Cantanhez National Park, Guinea-Bissau.
What the researchers observed
Bowland and colleagues used motion-activated cameras in Cantanhez to film wild western chimpanzees that were not used to people. The animals were eating African breadfruit, which ferments naturally as it ripens and contains ethanol. The ethanol content was low, up to roughly 0.6 per cent by volume in the samples reported. However, some of the feeding was social. The cameras recorded ten occasions on which chimpanzees shared the fruit, involving 17 individuals of both sexes and all age groups. In most cases the sharing was passive: an animal holding fruit let others feed from it.
Observed, and not shown
Observed: chimpanzees ate fermented fruit with low ethanol, and some shared it.
Not shown: that the animals became intoxicated, that they sought alcohol, or that sharing was meant to strengthen bonds. The authors treat the intent behind sharing as unclear.
Sharing, not intoxication
Even so, the researchers think drunkenness is unlikely at these levels, and the study does not report drunken behaviour. They also say that the effect of alcohol on chimpanzee metabolism is unknown, and that low levels across many fruits could add up. Earlier popular versions of the story spoke of mild effects such as delayed nest building or extra playfulness, but that is not what the paper shows, so do not repeat it in an answer. The solid point is the pattern of feeding and sharing.
The drunken monkey hypothesis
The finding is often linked to Robert Dudley’s "drunken monkey" hypothesis. It proposes that primate attraction to the smell and taste of ethanol is ancient, because low levels of alcohol signal ripe, calorie-rich fruit. On this view a mild pull towards fermenting fruit is an evolved foraging cue, and human alcohol use may be a later cultural elaboration. The new study is consistent with that idea but does not prove it. It records behaviour at one site, not the reason it evolved.
Why anthropologists care
The value lies in the comparison. Shared meals strengthen human relationships, and chimpanzees sharing a valued food looks like a distant parallel. That weakens any sharp line between human and primate sociality, while the careful reading is that the study offers a hint about shared roots of commensality, the practice of eating together, and not direct evidence that sharing fermented fruit bonded the group.
Using it in UPSC Mains
Under Paper I, Section 1.5, which lists primate behaviour, use it as a vivid example of diet and food sharing. Frame it around commensality and cooperation, not alcohol, and close with the limits: a single site, a small number of sharing events, and unclear intent.
The nearest exam question is Forms of Primate Social Organisation (2022); food sharing illustrates cohesion within a group but does not answer that question on its own. More questions are in the Human Evolution and Primatology PYQs. For related reading, see The Diet That Shaped Human Evolution and Orangutans and Metabolic Flexibility. The wider syllabus map is in the Anthropology Optional complete guide.
Sources
University of Exeter news release on the study. Dudley, R., the "drunken monkey" hypothesis.