Natural creatures are the first creatures of Creation. Unlike any of the other creatures of Creation, they were not created from the chaos, but evolved from Creation itself. Like the fey, they have existed nowhere but in Creation. Like the Immortals, they only came to be, and survived, through will and luck.
Unlike the fey, they are diverse, practical, adaptable creatures. Unlike both fey and Immortals, they have no innate ability to manipulate chaos; magic does not come naturally to them, and although some have a knack for it, it is possible this only occurs because of some unknown fey ancestor.
Humans are natural creatures.