Shapeshifters are the legacy of Transmutation experiments. The only successful ones from the days before such experiments were banned. The unsuccessful ones died or were killed. All shapeshifters are humans with greater than normal levels of magical energy and the ability to take the form of one animal. These abilities (or 'the curse') is passed down through their offspring, often even with an otherwise mundane partner.
Most were originally experiments to create humans with a greater aptitude for magic. However others were experiments in transforming humans into animals to act as scouts or guards for mages. Both types of experiments resulted similar results.
While magical in nature, lycanthropes or shapeshifters can seldom become mages. Their 'inborn' magic blocking any other magic they try to use. A few exceptions ot this rule have existed.