The two processes must also be distinguished from each other in their relation to personal selection, for induced germinal selection will go on increasing until the maximum of variation corresponding to the nature of the external influences and of the determinants concerned is reached. Since _all_ the ids are equally affected and caused to vary in the same way, personal selection has nothing to take hold of, and the variation might go on intensifying even if it should become biologically prejudicial. But it is quite otherwise with spontaneous germinal selection, which has its roots not in all, but only in a majority of the ids. Here the variation may go on increasing by germinal selection alone, but only until it acquires a positive or negative biological value, that is, until it becomes advantageous or prejudicial to the life of the individual; then personal selection intervenes and decides whether it is to go on increasing or not. Spontaneous germinal selection can therefore only lead to the general variation of a whole species when it is supplemented by some external factor such as, especially, the utility of the variation. This does not imply, however, that indifferent variations of large amount could not arise through spontaneous germinal selection, but they would remain confined to a small number of individuals, and would sooner or later disappear again. The congenital deformities of Man may in part fall under this category. If, for instance, certain determinants are, by reason of specially favourable local nutritive conditions, maintained for a long time in progressive variation, they will become so strong that the part which they determine will turn out excessive, perhaps double. Hereditary polydactylism in Man may perhaps be explained on this principle, and I had already referred it to the more rapid growth and duplication of certain determinants of the germ even before formulating the idea of germinal selection. In this I was at one with the pathologist Ernst Ziegler, who had designated polydactylism as a germ-variation, and in contrast to others had not interpreted it in an atavistic sense, as a reversion to unknown six-fingered ancestors. All excessive or defective hereditary malformations may be referred to germinal selection alone, that is, to the long-continued progressive or regressive variation of particular determinant-groups in a majority of ids.