People have toenails in order to meet their locomotive needs as primates. Humans' nails are what remains of their once very important claws. As humans evolved, they needed to make more intricate motions and thus have nails that were smaller and thinner than claws.
In addition to facilitating motion needs, toenails can provide insight into a person's overall health. If toenails exhibit discoloration or other anomalies, it is a good indication that the individual is in need of medical assistance. For example, malnutrition can be identified by a discoloration of the nail color. This is another adaptive characteristic of toenails.