GERMINAL SELECTION 137 



showed that the southern form can be artificially produced by 

 warmth, and the interpretation must be that the direct influence 

 of higher temperature affects the quality of the nutritive fluids in 

 the germ-plasm, and thereby at the same time the determinants of 

 one or more kinds of wing-scales are caused to vary in all the ids 

 in the same direction, in such a fashion that the}^ give rise to 

 black scales instead of the former red-gold ones. It is thus certain 

 that there are external influences which cause particular determinants 

 to vary in a particular manner. I call this form of germinal variation 

 ' induced ' germinal selection, and contrast it with ' spontaneous ' 

 selection, which is caused, not by extra-germinal influences, but by 

 the chances of the intra-germinal nutritive conditions, and which 

 will, therefore, not readily occur at the same time in all the ids of 

 a germ-plasm, and so will not give rise to variation of the same 

 kind in the homologous determinants of all the ids. 



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 Ijiological 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 varia- 

 tion, they will become so strong that the part which they determine 

 will turn out excessive, perhaps double. Hereditary polydactylism 



