INDIFFERENT VARIATIONS CAN CHARACTERISE SPECIES 137 



dependence on a primary variation wHcli is a biological charac- 

 teristic of tlie species as a whole, the secondary variation will 

 likewise become a characteristic of the species, though only a 

 secondary and morphological one. 



But there are cases of a variation being produced among all the 

 individuals of a species, and thus becoming a characteristic of 

 the whole species, though it is not of biological value in the 

 struggle for existence. As a rule, however, as we have said, a 

 secondary variation is restricted to a limited number of indi- 

 viduals, and is eventually suppressed as a result of amphimixis 

 — as we see often in the case of abnormahties and monstrosities. 

 And this is readily intelligible when we remember that perturba- 

 tions of the intragerminal nutrition, which are the source of 

 such variations, may afiect, in the germ-plasm of one individual, 

 the determinant A, in that of another the determiaant B, and 

 so forth; and when we recollect, further, that a majority of 

 identical determinants in a majority of ids must vary in the same 

 direction in the germ-plasm of every member of the species, before 

 a variation can become a characteristic of that species. 



Thus, if a biologically indifferent variation is to become a 

 characteristic of a species, there must be some condition which 

 acts in an identical manner on every individual of the species. 

 Obviously such a condition can only be foimd in the environment 

 in which the whole species Hves, and to which the whole species 

 is exposed. The action of the environment can therefore produce 

 such variations, which are not, strictly speaking, adaptations, for 

 they are not of biological importance. The most important of 

 these enviroimiental conditions are climate and food. 



Two questions at once present themselves for consideration : 

 in the first place, to what extent are such environmental condi- 

 tions capable of affecting the soma of the individual ? It is 

 evident that diet influences somatic development — that certain 

 foods tend to fatten, certain others to reduce the size of the body. 

 Experiments made on dogs belonging to the same litter, some 



