Has anyone thought why we need nails? Are these proof of claws we didn't need anymore or what?
And does this mean nail-biting was a natural ancestor activity? Perhaps to sharpen teeth?
"from evolutionary viewpoint, the limbs of all mammals end in a hardened structure - the hoof or claw. this hard structure serves the protect the limb from excessive wear (as in the hoof), or can be used as a tool for digging or as a weapon for overall protection (as in the claw). This arrangement has proved so useful, that every mammal has these items, or their equivalent, and evolution has acted to eliminate all genetic variation that would prevent their development.
So, evolutionary history has dictated that we must have a "hard thing" at the end of our fingers and toes.
When primates evolved, one of their defining differences was the
transformation of the claw into a nail. some types of less derived primates shave a few claws, but all primates still have a nail-like structure at the end of their fingers and toes). Primates manipulate their environment by grasping things and claws can get in the way of grasping and fine manipulation (same with long fingernails). Because primates tend grasp things (tree limbs, etc.) with both their hand and their feet it was advantageous to transform all of the claws into nails. Nails still provide some of the protective function of claws, but are not as effective as digging tools or weapons (try having a scratching match with your pet cat to verify this)."