Anonychia is the absence of fingernails or toenails, an anomaly which may be the result of a congenital ectodermal defect, ichthyosis, severe infection, severe allergic contact dermatitis, self-inflicted trauma, Raynaud phenomenon, lichen planus, epidermolysis bullosa, or severe exfoliative diseases.
Photo via the IAF subreddit, where this was said to be a case of anonychia congenita. I've always thought that humans would eventually evolve to eliminate toenails, which are vestigial appendages dating from the time when claws were useful. I can think of no useful purpose for a toenail, and don't think humans will miss them. Fingernails OTOH have a variety of uses.