344 DARWINISM AND THE PROBLEMS OF LIFE 



selection alone does not suffice to explain the origin of 

 species, and that we are compelled to postulate a pur- 

 posive internal formative energy in organisms. But 

 before we deal with these writers, we will describe a 

 recent theory which does not directly reject natural 

 selection, but greatly restricts its sphere of influence. 

 This is the "mutation theory" of the botanist, Hugo 

 de Vries. 



De Vries questions especially whether the actual forms 

 of life are due to ordinary variations. He says that 

 they are not inherited pure, and appeals to artificial 

 selection, as, for instance, in many kinds of grain. These 

 are never independent of selection, because as soon as 

 cultivators cease to watch and select them, they quickly 

 return to the parental species. Thus no character can 

 be fixed by natural selection to such an extent that it 

 will remain as a permanent quality of the new species 

 when selection has ceased. 



There is a second reason why natural selection cannot 

 have created the actual forms of life from variations. 

 The variations, he says, are restricted ; they cannot 

 increase indefinitely, and can at the most only double 

 the original character. We have, for instance, con- 

 siderably increased the amount of sugar in the beet 

 by selection, but that is all. Further, there has been 

 no increase in the size of gooseberries since 1852, 

 though one cannot see any reason why they should 

 not have become as large as pumpkins. There must 

 be an internal limit to variability. 



Hence de Vries believes that ordinary variations 

 cannot have produced the actual species. They must 



