Species

All people begin their lives as humans. Once they reach a certain level of Skill, they become eligible to change to a different species. Each species has specific Prerequisites. The person has an instinctive sense of which species are available to them and makes a conscious choice which they wish to become. After further improvement in Skill, this window closes. At that point, the transformation is complete or the opportunity to become non-human lost. Each species has its own set of Perks (with some overlap). The human species only receives these after this window has closed. When knowledge of a particular species and its prerequisites is lost, it is effectively extinct.