Nose-picking primates spark scientific quest

It is a biological mission that began with a chance encounter with a lemur that was picking its nose.

It wasn't just any lemur; an aye-aye was filmed by Prof Anne-Claire Fabre from the University of Bern burying its elongated finger in its nostril.

"I wanted to know where is this finger going?" she told the BBC.

The meeting at Duke Lemur Center in the US, led Prof Fabre and her colleagues to question the evolutionary origins of the habit.

Aye-ayes are nocturnal primates found only in Madagascar. They are famous for their strange, skinny, long fingers, which they use to fish grubs out of branches.

"It was inserting the entire length and, [when you look at] the length of its head, it was like - where is it going?" she recalled. "I wondered - is it inserting it into its brain? It was so weird and seemed impossible."

The question intrigued Prof Fabre so much that she conducted 3D anatomical analysis of the aye-aye's head, to reconstruct the seemingly impossible anatomy of the nose picking.

"It was going into the sinus and from the sinus into the throat and into the mouth," she explained.

With her colleagues, Prof Fabre searched the scientific literature for evidence of other animals that pick their noses. In a study they published in the Journal of Zoology, the team found 12 examples of primates caught in the nose-picking act.

At least a dozen species of primate, including orangutans, have been recorded picking their noses

As Prof Fabre, who is also curator of mammals at the Museum of Natural History in Bern, pointed out, there are very few studies that aim to understand why any animal, including humans, might have evolved the impulse to pick their nose.

"We really think this behaviour is understudied because it's really seen as a bad habit," explained Prof Fabre. Studies that investigate the behaviour in people have shed some light on how common the habit is, revealing that the majority of humans pick their nose often but are reluctant to admit it.

There are a few studies examining the cons - and possible pros - of nose picking. Some have pointed to its role in spreading harmful bacteria. But there is at least one study suggesting that picking your nose and eating it might actually be healthy for teeth, as people who picked their noses reported fewer cavities.

One study encouraged additional research by suggesting that the ingestion of nasal mucus could play an important role for the immune system, because of the immune proteins in the mucus.

Fundamentally, Prof Fabre says it is likely to have evolved for a reason and should be investigated.

"We have no idea about its functional role," she told the BBC. "And it could be advantageous."

Rather than being simply disgusting, it may have benefits for some species and since so many animals appear to share this habit, Prof Fabre said, "I think we really need to investigate it".