Eli5 why do humans get ingrown toenails?
In: 4
For many reasons, but shoes are a big part of it. Not only do shoes constrict your toes in a way that leads to ingrown nails. But they also make your feet sweat and get damp. This softens the skin, which allows nails to dig into it.
Cutting nails too short or rounding the edges can encourage the nail to grow into the skin instead of over it.
Because it didn’t kill us or stop us from mating so there was never any selective pressure towards better toenails. Evolution is a “good enough” generator, it tends towards making things good enough to no longer be subject to the selective driver causing the change.