Gibraltar Monkeys Eat Soil to Counteract Junk Food, Study Finds

The Barbary macaques of Gibraltar, a unique population of free-ranging primates in Europe and a symbol of British control, have revealed a fascinating adaptation to their increasingly Westernized diet. Researchers have documented these monkeys engaging in geophagy, or soil-eating, a behavior that appears to be a direct response to the consumption of human snacks like chocolate, crisps, and ice cream. This finding, published in Scientific Reports, highlights how these animals are attempting to self-medicate against the ill effects of junk food, much like humans might reach for antacids.

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We propose the idea that human food, being not adapted to their natural diet, triggers upset stomachs, and potentially microbiome disruption, of which negative effects are buffered by the soil components.

While the macaques receive designated food from local authorities, their close proximity to tourists often leads to them begging for or having their snacks stolen. The study observed that soil-eating was more frequent in groups with higher consumption of these human treats, which are high in sugar and fat and low in fiber. This suggests a direct correlation between poor dietary intake and the monkeys' natural inclination to consume soil.

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likely acts as antacids

Lead author Sylvain Lemoine from the University of Cambridge proposes that the soil's components, particularly clay, can buffer stomach acidity, adsorb toxins, and potentially help regulate their gut bacteria. This behavior is not unique to these macaques, as geophagy is observed in many animal species, including other primates. However, the Gibraltar macaques offer a compelling case study of how wildlife adapts to the challenges posed by human presence and dietary changes, demonstrating a remarkable, albeit rudimentary, form of self-care in the face of a modern diet.

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We don't know the exact action of soil within the gut, but soils, particularly those rich in clay, are known to alleviate gut pH (acidity), adsorb toxins, plaster the stomach and modify microbiome composition.