66 THE THEORY OF NATURAL SELECTION 



ance. Since all arguments in favour of the evolution 

 of species were incomplete unless some means by 

 which such an evolution could take place had been 

 suggested, Spencer adopted the Lamarckian theory of 

 modification, and to this he always firmly adhered, 

 though admitting the validity of natural selection as 

 an additional factor in the process. Some of Spencer's 

 arguments in favour of a belief in the inheritance of 

 acquired characters are well worth repetition, since 

 they have never been altogether refuted. 



Herbert Spencer's argument consisted mainly in the 

 enumeration of structures the origin of which cannot 

 be explained by natural selection. On the other hand, 

 the inheritance of acquired characters, if this form of 

 inheritance could be proved to have a real existence 

 as Spencer believed it could was shown to be a 

 perfectly adequate explanation of the origin of the 

 structures in question. In 1893, when Spencer up- 

 held his opinion for the last time, Bateson had not yet 

 pointed out that the facts of definite and discontinuous 

 variation afford an alternative way out of some of 

 these difficulties. In the absence, therefore, of any 

 other effective cause, the result of the argument 

 pointed strongly to the conclusion that the inheritance 

 of acquired characters must be a reality. 



The first of Spencer's arguments was based upon 

 the different powers of tactual discrimination which 

 are to be found in different parts of the human body- 

 The degree of this sensitiveness may be estimated by 

 the use of a pair of compassesj the points of which can 

 be set at different distances apart. It is then found 



