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We've all been there. You eat a Big Mac or an ice cream cone, and your stomach disagrees with some of the choices you've made. The same can be true for animals. A new study finds one group of junk food-eating monkeys is coping by eating dirt. NPR's Nate Rott reports.
NATE ROTT, BYLINE: If you're unfamiliar with the opportunism of the Barbary macaque, just jump on YouTube.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED PERSON #1: He's coming.
UNIDENTIFIED PERSON #2: Oh, he's got your bag. He's (inaudible).
UNIDENTIFIED PERSON #3: Oh, he got your glasses.
UNIDENTIFIED PERSON #4: Keep all your jewelries (ph).
UNIDENTIFIED PERSON #3: Quick. Got your glasses.
ROTT: They live in Gibraltar, on the southern coast of Spain, and they're the only wild monkeys in Europe, transplanted from North Africa centuries ago. So they draw a lot of tourists.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED PERSON #5: Oh, look. (Inaudible).
UNIDENTIFIED PERSON #6: (Inaudible).
ROTT: And the snack-packing tourists draw them.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED PERSON #5: He did. He's got ice cream (laughter).
ROTT: This daily mishmash of people and primates in a small area drew the attention of Sylvain Lemoine, an anthropologist at the University of Cambridge in the U.K. Since 2022, he and his students have been studying Gibraltar's macaques.
SYLVAIN LEMOINE: We go regularly twice a year, summer and winter, for - yeah - population monitoring and kind of long-term behavioral data collections.
ROTT: And almost immediately, one particular behavior stuck out. Some of the monkeys were regularly seen eating soil - clay and dirt - what scientists call geophagy.
LEMOINE: Earth eating or soil eating - geophagy - is a relatively common behavior across animals. It has been observed from birds to many mammal species.
ROTT: Even amongst humans. Sera Young wrote a book on the topic in 2012.
SERA YOUNG: The overarching umbrella term is called pica, and pica is nonfood cravings.
ROTT: Cravings for things like earth or starch or chalk.
YOUNG: There's also pagophagy, which is ice. Pagos means hard in Greek.
ROTT: Young, an anthropologist at Northwestern University, did an entire Ph.D.trying to understand why people have these cravings.
YOUNG: I wrote a really long paper with my boyfriend at the time, now husband.
ROTT: (Laughter) Hey.
YOUNG: Hey, hey. The things you do for love. You help your girlfriend, like, catalogue geophagic reports (laughter).
ROTT: And she says she quickly realized that if so many animals were doing this too, there had to be a reason.
YOUNG: Humans do lots of stuff for no good reason, but animals don't.
ROTT: And the most promising explanation she arrived at is that eating something like soil could help soothe an upset stomach.
YOUNG: I don't know how many clay mud masks you've applied in your life.
ROTT: Can there ever really be too many?
YOUNG: That's a great point. And so these - clay is really good at absorbing toxins.
ROTT: From your skin. The same, she says, may be true for your gut, which brings us back to Lemoine's study of Barbary macaques, where it became clear through observations that some groups of the monkeys were eating much more soil than others.
LEMOINE: And these groups are also interacting much more with people.
ROTT: Those are the ones higher up on the Rock of Gibraltar, closer to the vistas and unwatched ice cream bars. The only group of macaques they never saw eat soil was one that didn't interact with humans at all. Lemoine's findings, published in the journal Scientific Reports, suggest that the soil-eating may be an adaptation the monkeys are using to buffer their guts against all the available junk food.
LEMOINE: It really exemplifies the behavioral flexibility of the primates.
ROTT: And it suggests the behavior is being shared amongst the monkeys - that they're now showing each other which dirt to eat. A new tradition in a candy bar-rich world. Nate Rott, NPR News.
(SOUNDBITE OF FREDDIE GIBBS & MADLIB SONG, "GAT DAMN (INSTRUMENTAL)") Transcript provided by NPR, Copyright NPR.
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