Gibraltar macaques are self-medicating with dirt to help them digest human. junk food

Monkeys Resort to Eating Dirt to Cope with Tourist Junk Food

By Adam Kovac edited by Claire Cameron

Tourists in Gibraltar, known for feeding the local macaques junk food, might be causing the monkeys to feel queasy. Consequently, these macaques have started eating dirt to counteract the digestive issues from consuming too many sugary, fatty, and salty snacks, according to a recent study.

Gibraltar, a British territory, is home to Europe’s only wild Barbary macaques, making them a significant tourist attraction. However, the foods tourists provide are vastly different from their natural diet, which consists mainly of seeds, fruits, and vegetables.

A new study published in Scientific Reports by University of Cambridge biological anthropologist Sylvain Lemoine and his team reveals that these macaques have been observed eating soil and clay, a behavior known as geophagy. While this behavior has been documented in humans, certain birds, and other animals, it is the first time it has been formally recorded in Gibraltar’s macaques.

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The occurrence of geophagy among the macaques was not isolated. The researchers documented 46 instances of this behavior over 612 hours of observation across nine locations, involving at least 44 individual monkeys out of the approximately 230 in the region. The study indicates that this behavior is more common among Gibraltar’s macaques compared to other primates known to occasionally eat soil.

Both male and female macaques from various groups were seen eating dirt throughout the year, particularly in tourist-heavy areas.

Researchers concluded that tourists are likely giving the macaques so many high-calorie, salty, and fatty snacks that the animals turn to eating dirt to self-medicate. Consuming soil might help them obtain additional minerals and bacteria, and also combat nausea and diarrhea by creating a digestive barrier. The scientists estimate that such junk food constitutes nearly 20% of the monkeys’ eating time.

Lemoine stated in a statement that the macaques likely began eating soil to counteract the effects of high-energy, low-fiber snacks, which can cause gastric issues in some primates.

The monkeys’ preference for junk food mirrors the biological drive in humans to consume energy-dense fats and sugars. “Humans evolved to seek out and store energy-dense fats and sugars to survive periods of scarcity, leading us to crave high-calorie junk food,” Lemoine said. “The availability of human junk food could trigger this same evolutionary mechanism in macaques.”

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