Picking your nose (not to mention eating what you pick) is not accepted in polite company. However, research shows that most people actually frequently indulge in this activity. And we are not the only animals picking our noses (in scientific language this is called rhinotillexis) and eating our own mucus (scientifically called mucophagy). 12 species of primates have been observed engaging in these activities. Among them are our closest relatives: chimpanzees and bonobos, but also gorillas and orangutans and among monkeys: macaques and capuchins do it.
Recently, scientists observed nose-picking and snot-eating in the aye-aye – a lemur-like primate and also the most distantly related to us species of the currently known nose-picking “club”.
To pick its nose, the aye-aye uses its middle finger, which is thin, mobile and much longer than the other fingers. The animal inserts the entire finger into its nose and then licks it. Analysis of the aye-aye’s skull suggests that, when picking its nose, its finger reaches all the way down to its throat.
What all known nose-picking animals have in common is that they can move their fingers independently and have well-developed manipulative abilities. This allows them to not only manipulate the finger in their nose but even to use tools instead. Macaques and capuchins, for example, regularly use sticks.
Because picking one’s nose along with eating what one picks is so widespread among primates, scientists wonder if there is any benefit to these activities.
Perhaps it is simply a matter of cleaning the nose of accumulated mucus? But that doesn’t explain eating it afterwards. Some scientists suggest that eating one’s own snot acts a bit like self-vaccination, activating the immune system. On the other hand, others have shown that picking one’s nose helps bacteria to spread up the nose and down the throat, which tends to promote infections. Other studies suggest that eating snot may prevent bacteria from sticking to teeth and help maintain oral hygiene. Or perhaps eating nasal secretions is simply pleasurable? It has properties that are attractive to humans: it is salty, a little crunchy and generally has a pleasant texture – even if not everyone would admit it.
So far, these are mainly hypotheses and there is still no conclusive evidence for any of them. It is also unclear why the aye-aye puts his finger all the way down its throat. A lot of work still awaits scientists interested in nose-picking.
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Photo: nomis-simon – https://www.flickr.com/photos/nomissimon/15819070729/, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=42890351