228 THE PERPETUATION OF ADAPTATIONS 



This principle, advocated by Weismann leaves unexplained the 

 origin of the factors in the germ plasm, but interprets the 

 changes that may arise as due to shuffling about of the charac- 

 ters already present. Other biologists interpret amphimixis 

 as bringing about the exactly opposite result, viz., keeping the 

 race true to type and preventing variations. 



Mutations. A number of biologists believe that new types 

 arise suddenly, by jumps or mutations, which first appear as 

 freaks of nature or " sports. " The botanist de Vries discovered 

 a variety of primrose which underwent a spontaneous change of 

 type sufficiently well marked to make of it a new variety if not a 

 new species. It bred true to its type and showed no tendency 

 to revert to the ancestral form. De Vries concluded and many 

 biologists agree with him, that freaks or sports appear infre-^ 

 quently in the history of every species and serve as centers of 

 departure from old types. Such mutations were known to 

 Darwin and the earlier evolutionists, the race of Ancon sheep 

 being an historic example. 



Mutations may be due to the chance union of recessive char- 

 acteristics, which, as in Prof. Morgan's flies would be lost again 

 by promiscuous or indiscriminate breeding. Prof. Tower has 

 been able to breed in the laboratory distinct types of the potato 

 beetle which differ markedly from the ancestral type from which 

 they sprang, and he has found the same distinct types existing 

 wild in nature and regarded as different species. Here an 

 experiment was performed in the laboratory which had been 

 done on a larger scale in nature, with the advantage in the 

 laboratory because the starting point, a mutant, was known. 

 But again the result may be interpreted as due to shifting of 

 germinal characteristics followed by discriminating breed- 

 ing. 



If, in any of these cases, the variation is useful to the organism 

 in its struggle for existence, the chances of living and of mating 

 are increased which would result in the numerical increase of the 

 mutant type until possibly the ancestral or original type is 

 crowded out. Thus by natural selection a new species and one 

 better adapted to the environment would result. Or it is 



