336 ACTION OF NATURAL SELECTION 



with the gradual evolution thereby brought about. 

 The fundamental importance of variations in the evo- 

 lutionary process has been dwelt on again and again by 

 Darwin, by Wallace, and by most of the subsequent 

 writers on the subject, and as this doctrine is so uni- 

 versally admitted, it is unnecessary to discuss it any 

 further here. At the present day, however, there ap- 

 pears to be a considerable amount of scepticism among 

 some men of science as to the extreme importance 

 which has been generally attached to the agency of 

 Natural Selection. Some, such as Driesch, have even 

 denied its existence altogether, whilst many others hold 

 that its existence has never been demonstrated. They 

 hold with Lord Salisbury * that " no man, as far as 

 we know, has ever seen it at work." The evidence 

 to be adduced will show, I believe, that this statement 

 is erroneous, but even if it be correct, it cannot dis- 

 prove the theory, the validity of which seems to me a 

 logical necessity. Thus, granted the geometrical rate 

 of increase possessed by all organisms, and the severe 

 struggle for existence thereby entailed; granted that 

 all organisms show individual variations, and, to a con- 

 siderable extent, hereditary transmission of such varia- 

 tions, then it must follow that, on an average, more of 

 the organisms possessing favourable variations better 

 adapted to their environment will survive than of those 

 possessing less favourable ones. That is to say, the 

 species will become gradually modified by the action of 

 Natural Selection. 



Numerical evidence in support of the theory of 

 Natural Selection has been obtained only quite 

 * "Presidential Address, British Association," 1894. 



