ISTM that they would have to, since the fingernail doesn’t know whether it’s been cut. So if fingernails which are trimmed keep on growing, then fingernails which are not trimmed should keep growing forever too. This would imply that if people never cut their fingernails, that they would eventually grow to several feet long.
But OTOH, this seems pretty paralyzing, and hardly makes sense as a beneficial evolutonary adaption. What woud primitive peoples have done? And what’s the situation with other primates - do they have some way of dealing with this, or are their nails different?
Eventually they break. People need to use their hands and that means putting strain on excessively long nails. Better to trim them yourself before jagged, broken nails become a health issue.
How other species deal with this is the same way humans likely dealt with it thousands of years ago - the more you use your hands, the more your nails will naturally get worn down. In the worst case, people can bite them down as well (some may consider it a bad habit, but habitual nail biters don’t need to trim their nails very frequently). We see this with dogs, cats, rabbits (for their teeth), etc. Use your nails frequently and they naturally wear down.
They do keep growing forever- which is how some people do end up with 2 ft long fingernails. But in order for them to get that long, they not only need to keep growing - they also need not to break or get worn down.
If the fingernail were all living tissue, growing by adding new cells at the end, it would be straightforward for the nailbed tissue to signal to the nail tissue so it would know when it had reached the end of the finger. But since it grows by adding new cells at the root and pushing out hardened dead cells, that developmental model won’t work.
It’s easy to see that a layer of regenerated protective hardened dead cells on your digits can be an advantage. You’re arguing that evolution should have evolved an “on demand” mechanism for replacement, so that they grow only when they need to be replaced. Evolution has settled on a continual replacement mechanism, presumably because a more complex “on demand” replacement mechanism is difficult to evolve and/or just isn’t required. In the ancestral environment, wear and tear was presumably fairly constant, or it just wasn’t a big deal to have them break off or be bitten back if they occasionally got to long.
There a nice close-up of a chimp hand here. The natural manicure process seems to be working fine.
What inspired this thread is that for whatever reason I have not cut my fingernails in three weeks. They are already longer than that chimpanzee’s, and don’t show any signs of being worn down. What type of once-common activity might contribute to significant wearing down of fingernails?
As to breaking, one actually did break. But in this case - as with similar cases in the past - they don’t break off cleanly. Rather the crack typically is in a manner which is sort of perpendicular and extends into the area where it’s attached to my finger. If that actually separates, it would be painful, and it requires careful cutting and filing to avoid that. So I don’t know if that’s so practical as a routine matter.
What about comparable features of non-primates? Claws of felines, talons of birds etc. Same process?
If you’re digging in the dirt all day, that’ll help wear them down. But even so, if you don’t trim them otherwise, they’ll just break eventually. And usually not very cleanly. That’s why we trim. Humans have been trimming their nails for thousands of years for good reason.
Cats scratch all the time - there’s no shortage of scratching posts for sale, partly to keep their claws trimmed.
Likewise, rodents have to constantly grind their teeth or they’ll run into problems.
Actually, cats do periodically shed their claws, especially the hind ones, which I do not trim. The new one has already grown in when the old one drops off.
I use my hands routinely to do all sorts of things, ranging from typing to kitchen work to minor mechanical work to planting/weeding/etc. out in the fields. If I don’t keep them cut quite short, they break – and often break before I get around to cutting them.
It’s true that they rarely break cleanly; which is one of the reasons I carry a swiss army knife, for the scissors. But my teeth work pretty well too, so I expect that’s what people used before scissors. And all sorts of things might have worked for nail files – rough surfaced rocks, dried clay, rough bark.
Felines scratch on trees or similar surfaces if available. Scratching on something frequently is routine behavior – that’s why people with indoor-only cats buy scratching posts. Dogs wear theirs down just by walking; old or inactive dogs may not wear theirs down enough and may need them trimmed.
That’s not the whole claw, it’s just an outer layer.
Guinness won’t give you the straight dope on whether fingernails grow after death, but Ripley’s will - and nails do grow postmortem, a whole 3 microns in the time it takes your nail matrix cells to die after brain death (my nails just keep on growing because I am of the Undead).
"It strikes me that these nails will continue to grow like lean fantastic cellar-plants long after Kemmerich breathes no more. I see the picture before me. They twist themselves into corkscrews and grow and grow, and with them the hair on the decaying skull, just like grass in a good soil, just like grass, how can it be possible?”—from All Quiet on the Western Front
The Wiki article you cited does say that, but if you look at their source, it doesn’t say anything about constant use offsetting that. (What type of use might the creature be constantly doing with teeth like that?)
It looks rather that whether its skull gets impaled is dependent on age and direction.
Right. I was responding to the suggestion that in more primitive times nails might have worn down and thus not needed to be cut. So I was wondering what type of activity might have had this great of an impact, but whatever it was it doesn’t seem like something which is done today. It sounds like whatever you’re doing these days does not wear your nails down that much if at all, so you might agree with me too.
Part of what I was trying to say, if not very clearly, was that they wouldn’t have needed to be cut in the modern fashion, because they would have broken off, with the assistance of chewing when necessary.
Whether people also ground their nails down, deliberately or otherwise, against rocks and/or rough soil and/or plant material I don’t know.
I am going to guess that your nails have never grown much beyond your fingertips since you say you haven’t cut them in three weeks and they are longer than the chimp’s. Right now, most of my nails extend beyond my fingertips - only most, because the two that are shorter broke when I was doing some ordinary work. Not really sure what it was - maybe they were in water too long and got softened up and then I almost dropped a dish but caught it in a way that broke the nail, maybe I was weeding and broke it on a rock or maybe I was doing some hand laundry and my nail got snagged on a piece of clothing. Long nails in some ( maybe most) cultures) were a symbol of wealth , because someone doing manual labor would not be able to grow their nails long.
When I was a kid we had a parakeet, and we had to always keep a cuttlebone in his cage.
It was a dietary aid (good source of calcium) but also helped keep his beak from overgrowing. We also had wooden things for him to chew on as well. That’s because bird beaks keep growing. It’s not just mammals that have that issue.
Normally, a healthy bird’s daily activities include plenty of chewing, eating, and foraging, which helps to naturally keep the beak ground down to the proper length and shape. Birds are often observed rubbing their beaks on rough surfaces, which also helps to maintain the beak.
