POST-DARWINIAN VIEWS 67 



underlying premise is that the process of evolution and 

 of propagation is purely mechanical, and can only be 

 correctly explained in mechanical terms. The varia- 

 tions which appear in offspring are not due to the trans- 

 mission of acquired characters, but to the diverse 

 combinations and workings of the characters contained 

 in the germ-cells of the male and female parents. 



The new theory gained wide acceptance, and was 

 thought to strengthen the Darwinian hypothesis and 

 to estabhsh the practically exclusive value of natural 

 selection in evolution. Those who have taken this 

 position are called neo-Darwinians. The controversy 

 which followed was a vigorous one, and you will find 

 it worth while to read the debate between Weismann 

 and Spencer, which is found in several articles contrib- 

 uted by them to the Contemporary Review in 1893 and 

 1894. The result has been that, while beHef in the 

 inheritance of acquired characters has been much 

 weakened, the correctness of the neo-Darwinian posi- 

 tion has not been generally acknowledged. On the 

 contrary, its supporters have been obliged to make 

 compromising concessions. Professor Weismann felt 

 forced to acknowledge that natural selection as pre- 

 viously set forth does not explain the earlier stages 

 of development of useful variations; and in 1892 he 

 broached the germ-plasm theory.^ This theory treats 

 the cells as made up of a multitude of smaller particles, 



^ Exhibited in his Evolution Theory, Lees, xvii-xix, xxii. Cf. 

 R. H. Lock, op. cit., pp. 259-263; V. L. Kellogg, Darwinism 

 To-day, pp. 193-201. 



