MUTATIONS AND EVOLUTION. 307 



of view of the mutation theory. It explains, in a very simple 

 way, the existence of numerous species — characters that are en- 

 tirely useless." And again in 1918* : " If related species have 

 many genes in common they may be expected to produce at times 

 the same mutants." 



Prof. Bateson is, however, wholly opposed to mass or racial 

 evolution of this character. In his Australian address (p. 301) 

 he remarks : " Modern research lends not the smallest encourage- 

 ment or sanction to the view that gradual evolution occurs by the 

 transformation of masses of individuals, though that fancy has 

 fixed itself on popular imagination." The broad survey which 

 we are able to take of the ostrich, practically continental in its 

 extent and unlimited as regards numbers, may well lead us to 

 different conclusions. In the next section, dealing with the 

 retrogressive mutations in the ostrich, we appear to have evidence 

 that corresponding germinal changes have been, and are being, 

 effected independently throughout the entire race. 



SUCCESSIONAL MuTATIONS. 



Isolated, discontinuous mutations, whether large or small, 

 do not appear to have been the means whereby the more 

 fundamental features of organisms have arisen. They fail to 

 afford an explanation of the various intermediate phases of 

 development of structures and organs which confront the com- 

 parative anatornist and palseontolcgist who survey wide evolu- 

 tionary series. For the production of these, germinal changes 

 of a successional cumulative nature seem to be required, continued 

 with the same trend over long periods. The recurrence of the 

 same mutation throughout a race would give specific or generic 

 separation, but would not provide a sequential series in a definite 

 direction, of which we have so many instances in the animal 

 kingdom. 



In his article, " Evolution by Mutation," Prof. Morgan sees 

 the necessity for a successional series of changes, but regarding 

 the matter altogether from the Mendelian aspect, has a meagre 

 offering to make. To steer clear of any suspicion of a directive 

 force in the germ plasm, he submits (p. 50) the following as of 

 fundamental importance when evolution is treat.ed merely as a 

 phenomenon of chance: ^'Starting at any stage, the degree of 

 development of any character increases the probability of further 

 stages in the same direction. ... In this sense evolution is more 

 likely to take place along the lines already followed, if further 

 advantage is to be found in that direction. . . . The individual 

 multiplies itself, and a new mutant character that is advantageous 

 becomes established in a large number of individuals, or even in 

 all the individuals of the race. The number of individuals 



* "The Scientific Monthly," vol. 7, July, 1918, p. 47. 



