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Japanese macaques – which actually wash their food in salt water before consuming it – are a lot cleaner than other primates and have fewer parasites, a new study suggests.
Feelings of disgust may triggers cleanliness in all primates – including humans – which also leads to healthiness. Female macaques have especially avoided foods that looked disease bearing.
“There are a few other accounts of animals washing food in water, like captive chimpanzees and capuchins, which both seem to wash specifically to remove debris from food items,” Andrew MacIntosh, an associate professor at Kyoto University’s Primate Research Institute and Wildlife Research Center, said.
A recent study – conducted in European zoos – found that the animals tended to wash the foods that had been previously covered in experimental debris by the researchers.
The new study – published in the journal Biology Letters – analysed the behaviour of Japanese macaques. Based on the observations, the monkeys spent most of their time grooming each other, and were also seen washing sweet potatoes in salt water.
Aside from monitoring cleanliness behaviours in Japanese macaques, Cécile Sarabian, co-author of the study and a PhD Student at Kyoto University, along with MacIntosh decided to conduct an experiment in which they placed faux faeces and real faeces in the monkey’s habitat.
They placed a peanut or a grain of wheat on both the real and fake faeces, to attract the monkeys.
Female monkey were especially turned off by the faeces covered foods. They passed up the wheat, but decided to go for the peanuts. It seems as though these monkeys have the ability to weigh the benefits versus risks when choosing what to eat.
Nature and nurture may both lead to good hygiene. According to Sarabian, the animals that are more cautious when it comes to potential contaminants may achieve a reproductive advantage, as opposed to those that are not as cautious.
Valerie Curtis of the London School of Hygiene and Tropical Medicine’s Hygiene Center said that she also had a theory as to how disgust is an evolutionary mechanism that prevents infections in animals.
Hygienic behaviour observations have been made in the past, however this is the first study that actually demonstrates the function of hygiene in primates, Curtis added.
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