Human is the default classification of all characters. As a default, characters should not be added to this category.
Categories that are for sub-species of humanity - like Atlanteans - or or human/other hybrids should have "Humans" added as a category.
If you find a character in the database that is not human and not categorized as an alien species or human sub-species, please edit that character's page adding the appropriate type "AlienRace". Metahumans is an exception and should only be added as a category, not and AlienRace.