I would suspect they'd simply be worn down due to physical labour. Like how we have to trim a pet dog's nails, but in general, a dog in the wild doesn't need them trimmed because they wear down due to walking, hunting, digging, etc.
Interesting question, I hadn't thought about that! I just cut my nails with a regular nail clipper; not gonna start biting them in the name of re-enactment ;) I think it's come to be regarded as less socially acceptable because of sanitary issues involved with spitting bits of fingernails wherever.
I don't think there's anything innately bad about biting your nails. It's just that the people who do it do it as a nervous habit and end up biting them down too far. Paleo man probably did bite them though, when they didn't end up getting broken off by his daily activities.
Ever since I was a kids I used to pick at the side of my nails and then peel the ends off. The grain of the nail runs in a curve around the end of your finger rather than straight across so the nails splits in a curve around the end of your nail therefore not tearing into the skin (unless you pick too far down. This works on toenails too.
Only sine I became an adult did I start using nail clippers.
It must have been alien technology,or there women bit them off for them because everyone knows when man has long toenails he can get a better grip while making love,so either aliens did it for them or there women bit them off for them or they bit each others off like apes do when they groom each other.