VI DIFFICULTIES AXD OBJECTIOXS 143 



it as one of the diflSculties which can alone be overcome by his 

 theory of physiological selection. He urges, that the same 

 variation does not occur simultaneously in a number of 

 individuals inhabiting the same area, and that it is mere 

 assumption to say it does ; Avhile he admits that " if the 

 assumption Avere granted there would be an end of the present 

 difficulty ; for if a sufficient luimber of individuals were thus 

 simultaneously and similarly modified, there need be no longer 

 any danger of the variety becoming swamped by intercrossing.'' 

 I must again refer my readers to my third chapter for the 

 proof that such simultaneous variability is not an assumption 

 but a fact ; but, even admitting this to be proved, the problem 

 is not altogether solved, and there is so much misconception 

 regarding variation, and the actual process of the origin of 

 new species is so obscure, that some further discussion and 

 elucidation of the subject are desirable. 



In one of the j^reliminary chapters of Mr. Seebohm's recent 

 work on the Charadriidce, he discusses the differentiation of 

 species ; and he expresses a rather widespread view among 

 naturalists AA'hen, speaking of the swamping effects of inter- 

 crossing, he adds : " This is unquestionably a very grave 

 difficulty, to my mind an absolutely fatal one, to the theory of 

 accidental variation." And in another passage he says : " The 

 simultaneous appearance, and its repetition in successive genera- 

 tions, of a beneficial variation, in a large number of indiAiduals in 

 the same locality, cannot possibly be ascribed to chance." These 

 remarks appear to me to exhibit an entire misconception of the 

 facts of variation as they actually occur, and as they have been 

 utilised by natural selection in the modification of species. I 

 have already shoAATi that every part of the organism, in common 

 species, does vary to a very considerable amount, in a large 

 number of indi^-iduals, and in the same locality ; the only point 

 that remains to be discussed is, whether any or most of these 

 variations are "beneficial." But every one of these variations 

 consists either in increase or diminution of size or power of the 

 organ or faculty that varies ; they can all be divided into a 

 more effective and a less effective group — that is, into one that 

 is more beneficial or less beneficial. If less size of body would 

 be beneficial, then, as half the variations in size are above and 

 half belpw the mean or existing standard of the species, there 



