Why do we bite our nails?
Why is nailbiting so common? Not piking one's nose or poking one's eye, but specifically biting one's nails? It is said that 30% of kids and 45% teenagers are nailbiting. It is unlikely that it stops there. When people are stressed it provides relief, and when they get bored it provides stimulation. Most of the ideas I found are meaningles neurophysiological lingo, but there are more substantive yet dubious "etiological" explanations like
...anxiety, stress, loneliness, imitation of other family member, heredity, inactivity, transference from a thumb-sucking habit, and poorly manicured nails. http://www.ncbi.nlm.nih.gov/pubmed/18675214?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_SingleItemSupl.Pubmed_Discovery_RA&linkpos=4&log$=relatedreviews&logdbfrom=pubmed
The simplest idea would be that we do it because apes do it in general. Nails grow and need to be taken care of. It turns out that nails generally wear down in great apes, but they habitually bite their own nails, perhaps in order to even this tear and wear -- or maybe sharpen their nails. Chimps in particular are vicious animals that use their nails for mauling each other and their prey.
Maybe we bite nails as a sharpening prelude to an aggression? That would explain why teenagers bite their nails more often than younger children. It would also explain why we bite nails when stressed (resolution of stress may involve a fight). To my surprise, I immediately found that there is indeed statistical correlation between nailbiting and oral aggression in teenagers
http://www.ncbi.nlm.nih.gov/pubmed/3401428
Nailbiting sometimes leads to bleeding. This makes sense: if nails are used to maul a peer, infecting the wounds with one's blood is a way to go. Another interesting fact is that girls appear to be more frequent nailbiters than boys
http://www.capmh.com/content/2/1/13
even among twins
...Nail-biting was practised by almost a third of the children of 338 twin pairs in this series. It was one and a half times as frequent in girls as in boys. About two-thirds of the monozygotic twin pairs were concordant for nail-biting compared with about one-third of the dizygotic pairs. http://www3.interscience.wiley.com/journal/119689090/abstract?CRETRY=1&SRETRY=0
Curiously, our women do like to show their long, sharp nails. Hmmm. Nailbiting in distress, making one's nails to look like claws - what that might be about? Why do we bite our nails?
...anxiety, stress, loneliness, imitation of other family member, heredity, inactivity, transference from a thumb-sucking habit, and poorly manicured nails. http://www.ncbi.nlm.nih.gov/pubmed/18675214?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_SingleItemSupl.Pubmed_Discovery_RA&linkpos=4&log$=relatedreviews&logdbfrom=pubmed
The simplest idea would be that we do it because apes do it in general. Nails grow and need to be taken care of. It turns out that nails generally wear down in great apes, but they habitually bite their own nails, perhaps in order to even this tear and wear -- or maybe sharpen their nails. Chimps in particular are vicious animals that use their nails for mauling each other and their prey.
Maybe we bite nails as a sharpening prelude to an aggression? That would explain why teenagers bite their nails more often than younger children. It would also explain why we bite nails when stressed (resolution of stress may involve a fight). To my surprise, I immediately found that there is indeed statistical correlation between nailbiting and oral aggression in teenagers
http://www.ncbi.nlm.nih.gov/pubmed/3401428
Nailbiting sometimes leads to bleeding. This makes sense: if nails are used to maul a peer, infecting the wounds with one's blood is a way to go. Another interesting fact is that girls appear to be more frequent nailbiters than boys
http://www.capmh.com/content/2/1/13
even among twins
...Nail-biting was practised by almost a third of the children of 338 twin pairs in this series. It was one and a half times as frequent in girls as in boys. About two-thirds of the monozygotic twin pairs were concordant for nail-biting compared with about one-third of the dizygotic pairs. http://www3.interscience.wiley.com/journal/119689090/abstract?CRETRY=1&SRETRY=0
Curiously, our women do like to show their long, sharp nails. Hmmm. Nailbiting in distress, making one's nails to look like claws - what that might be about? Why do we bite our nails?