Do all primates have to trim their fingernails in some way, or do some primates' fingernails wear off through natural use?
Also, is constant nail growth common to all primates?
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Both. Many primates bite their nails. Some do not. It's not species specific.
Chimpanzees, for example, usually bite their nails; some prefer to leave them alone. They do grow continuously, and nails not kept trimmed probably break off (looking at the thickness of those nails, I get the impression that this might be rather painful if they break too short.)
The caption for the picture below (taken from a chimpanzee sanctuary) states
Annie likes to pick Missy’s nose. Missy tolerates it but doesn’t seem to enjoy it. I don’t blame her – Annie doesn’t bite her nails down like the other chimps do.
They bite their toenails as well.
Why some human beings bite their nails? Because, they are primates - it is inherited way to treat our nails, called onychophagia. While normal in some primates (and this is the way they treat their nails), it is considered abnormal in human.