There are species that retain their characteristics even in conditions that are relatively different from their natural ones; other species in similar circumstances instead become extinct; otherwise what takes place is racial mixing with other elements in which no assimilation or real evolution occurs. The result of this interbreeding closely resembles Mendel’s laws concerning heredity: once it disappears in the phenotype, the primitive element survives in the form of a separated, latent heredity that is capable of cropping up in sporadic apparitions, even though it is always endowed with a character of heterogeneity in regard to the superior type.