MUTATIONS AND EVOLUTION 571 



not been able to produce new species by selecting slight varia- 

 tions, and thus It IS claimed that new species cannot be built up 

 by natural selection through the selection of slight variations 



Although Darwin's theory of natural selection is not accepted 

 as being entirely correct, it has not been discarded and it remains 

 for future investigations to determine just how much Darwin's 

 explanation falls short. 



Mutations and Evolution. — De Vries pointed out the impor- 

 tance of mutations in the formation of new species. He saw new 

 species of the Evening Prim rose arise through mutations. They 

 came into existence at one bound and were not built up through 

 a long process of selection. De Vries' idea is that species arise 

 suddenly and natural selection then determines whether they 

 shall survive or perish. The mutation theory is not out of har- 

 mony with Darwinism but holds a different idea as to the material 

 upon which natural selection works. According to Darwin's 

 theory, natural selection works on most all kinds of variations, 

 and slight variations are preserved by heredity and gradually 

 built up by natural selection. According to the mutation theory, 

 only mutations play any considerable part in the origin of new 

 species, and all natural selection has to do is to determine whether 

 the new species shall survive or perish. If the mutants are 

 adapted to their environ ment, they survive, multiply, and result 

 in a new type or species. If they are not adapted to the environ- 

 ment, they most likely perish. 



There is much evidence that many new types of plants and 

 animals have originated by mutations, but just how much muta- 

 tions have had to do with the origin of the multitudinous forms 

 of plants and animals now in existence we are not yet able to tell. 

 Germinal variations and Evolution. — The theory of germinal 

 variations was proposed by Weismann. In the discussion of 

 variations it was stated Weismann held that plants and animals 

 consist of two kinds of protoplasm. The protoplasm «f which 

 sperms and eggs are composed is germ-plasm. The protoplasm 

 of which all other parts of plants and animals are composed is 

 somatoplasm. It is germ-plasm which parents transmit to off- 

 spring. It is the only inheritable substance of the higher plants 

 and animals. It carries the determinants or genes that determine 

 characters. From the germ-plasm transmitted to each individual 

 there arises the somatoplasm out of which the body of the 



