In biology, organisms are classified in two ways; The Kingdom, which includes the animal, plant, fungi, bacteria, virus, and spirit kingdoms, and the Evolutionary Type, which includes Natural, Unnatural and Supernatural.
The Kingdom of a creature determines what sort of creature it is. For example, an Alphuffel would be in the Animal kingdom, since it has the biological make-up of an animal.
Organisms of the Natural Evolutionary Type are those who evolved purely by natural selection. That is, the individuals most fit to survive in their habitat tend to reproduce the most, eventually leading to the creation of new species. Most regular, everyday organisms, such as rumpkins and forglorns, fall under this category.
Organisms of the Unnatural Evolutionary Type are those which have been cultivated by sentient species such as humans or vistem. Sentient species can breed organisms with traits which they like and mold them to fit their own desires, often pulling them far away from their natural state. Unnatural type organisms include Candy Horses, Smilewheat, and Alphuffels. Since the invention of cloning and genetic engineering, a new subtype of Unnatural Evolution has been created called Advanced Unnatural Evolution. This is where sentient species go straight into the genomes of organisms and add and remove whatever genes they want.
Finally, there's Supernatural Evolution. Organisms of the Supernatural Evolutionary Type are those which have been moulded by magical forces of various types. These magical forces include, but are not limited to, witches and wizards, spirits, and deities. Creatures such as the Choiceling, Tea Spirits, and Roglama are examples of Supernaturally Evolved organisms. Supernaturally evolved creatures all have a certain magical aura which can be detected using a special device. This aura is called an S E field.
There is also a pseudo group called Unknown. This category includes, obviously, organisms whose evolutionary type is unknown. These are organisms who don't have a detectable S E Field, but are so different from all other organisms that Natural Evolution seems unlikely or impossible. This group includes creatures such as the Dirt Eater.