A monkey in Japan flosses its teeth with its hair, demonstrating that humans aren't the only animals that clean their teeth and invent tools to help with the task.
The flosser, a free-ranging, middle-aged, female Japanese macaque named Chonpe, may have come up with the tool and the idea, according to a new study that will appear in the January issue of Primates.
Lead author Jean-Baptiste Leca told Discovery News that dental flossing could have been a fortuitous yet "accidental byproduct of grooming."
Leca, a post-doctoral fellow at Kyoto University's Primate Research Institute, explained that "Japanese macaques sometimes bite into hair or pull it through their mouths to remove external parasites."
The hair might have become stuck in Chonpe's teeth, and as she drew the hairs out, "she may have noticed the presence of food remains attached to them."
"The immediate reward of licking the food remains off the hair may have encouraged her to repeat the behavior for the same effect in the future," he added.
Leca and colleagues Noelle Gunst and Michael Huffman noticed Chonpe's flossing while studying a population of Japanese macaques living at the Iwatayama Monkey Park in a mountainous region at the outskirts of Kyoto, Japan. Although the monkeys at the park are free to roam, he said they are provisioned with food several times a day and may therefore have more "free time on their hands."
Chonpe apparently used her time wisely, as she devised three different ways of flossing, Leca said.
For the first, called the "stretching with mouth technique," she utilizes her mouth to gently pull her still intact hair, or that of another monkey, while moving her head backwards and chattering her teeth to permit flossing.
The second method, called the "stretching with hand technique," is similar, with the main difference being that she holds onto the still-intact hair strand with her hand instead of her mouth.
The third "plucking technique" is the closest to human-style dental flossing. To do this, she pulls out strands of her own hair and, with her hands, runs the hair between her teeth to remove food particles.
Leca and his team first noticed this behavior four years ago, and only recently has it begun to spread to other members of Chonpe's troop.
He explained that 14-year-old, childless Chonpe only has two close kin: her mother and one sibling.
"Since the pathways of diffusion of most behavioral innovations by Japanese macaques involve at some point the spread among siblings and the downward vertical transmission from mother to offspring, this paucity in individuals closely related to the innovator may have limited opportunities for diffusion of dental flossing behavior," he said.
Chonpe is also a mid-ranking monkey, so she spends a lot of her day grooming others, which may have inspired her to perfect her methods. The researchers observed her rolling small stones in her hand while attempting to remove a spine stuck in her palm, so it's possible she is a particularly innovative individual.
Prior to this study, the use of twigs as toothpicks was reported in chimpanzees, bonobos and orangutans.
Kunio Watanabe and another Kyoto University team have also observed dental flossing in a troop of long-tailed macaques living around a Buddhist temple in Thailand, but those monkeys often interact with humans and even pull out human hair for use as dental floss.
Researchers hope to study the flossing behavior more in future, as it could help to explain how innovation might spread and become a common practice for primate species, including humans.