Metamorphosis
Metamorphosis is the biological process by which an individual organism undergoes a profound change in appearance from one stage to another as part of its development.
Many Kreatures are capable of metamorphosis. The first stage in a Kreature's metamorphic sequence is known as the null-form, and any subsequent stages are referred to as the meta-form, and will often differ from its previous stage in terms of its attributes, size, powers and rank. Kreatures which do not metamorphose are ametabolic. Aside from a handful of species which need to metamorphose to complete their reproductive cycle, most null-form Kreatures are neotenic, meaning they are able to achieve sexual maturity without metamorphosing.
All bioengineered null-form Kreatures are specifically designed to be duds by default, requiring the use of species-specific genetic patches to unlock their latent ability to transform into their next stage. This allows novice Tamers a wider selection of low-ranking Kreatures to choose from without the risk of it metamorphosing into something they might not have the proper license to own. Wild Kreatures are able to metamorphose unimpeded, and so are the unmodified offspring of bioengineered Kreatures.
It should go without saying that metamorphosis is distinct from evolution, which refers to heritable changes in the gene pool of a population over successive generations. Individuals do not evolve and evolution has no end goal, is not linear, and doesn't make organisms "superior" to their ancestors. Other mon-franchises' usage of the term is wrong wrong wrong!!!