 The immediate consequence of this theory was a new rigidity given to the concept of species that it had not possessed in the Aristotelian and Scholastic traditions. Preexistence theory reinforced a sharp distinction between “essential” and “accidental” properties to a degree not implied by the prior tradition. At the same time, preexistence theory made it difficult to explain obvious empirical phenomena, such as monstrosity, the regeneration of lost parts, the resemblances of offspring to both parents, evidence for geographical variation, racial differences, and the existence of hybrid forms such as the mule. It seemed necessary to attribute these anomalies to divine action at an original creation. These difficulties in the theory resulted in a variety of criticisms that were eventually to lead to the downfall of preexistence theory in its original form, although the theory was to have a long subsequent history through a modification of the “germ” theory (Detlefsen 2006; Roger 1963 [1997: chp. 7]; Roe 1981).