ABSTRACT
The main point which prevented investigators, like G. Cuvier and his disciples, from accepting a genetic connection between the present and previous animal and plant forms of different appearance, was the conviction that the organisms always retained their specific peculiarities. Breeding experiments show, in the first place, that under purposeful supervision of the reproduction very varied forms can arise, which often remain constant—as, for instance, dogs, cattle, pigeons, and the remarkable forms of the cabbage. As in ‘evolution,’ these alterations can certainly hardly be directly considered, but they show that the organism is no stubborn unchangeable form. It is not all deviations which appear in the progeny of the same animal or plant parents which can be imputed to the influence of changed environment. There are plants and animals which, precisely in the same habitat, or in the same region, often produce spontaneous deviations—that is, without a recognizable external cause.
