148 MEAXIXG OF THE SYSTEM. 



play a considerable part in his attempt to account for the origin of 

 varieties, with having accounted for everything by the struggle for 

 existence, and with having given too little prominence to the direct 

 influence of physical action on the mutation of forms. This 

 reproach seems to arise from a misapprehension. Darwin says 

 himself that the expression " chance," which he often uses to explain 

 the presence of any small alteration, is a totally incorrect expression, 

 and is only used to express our complete ignorance of the physical 

 reasons for such particular variation. 



If Darwin has by a series of considerations arrived at the conclu- 

 sion that the conditions of life, such as climate, nourishment, etc., 

 exercise but a small direct influence upon variability, since, for in- 

 stance, the same varieties have arisen under the most different 

 conditions, and different varieties under the same conditions, and 

 that the complex adaptation of organism to organism cannot be 

 produced by such influences, still he recognises in the alteration of 

 the vital conditions and the mode of nourishment the primary cause 

 of slight modifications of structure. But it is only natural selection 

 which accumulates those alterations, so that they become appreciable, to 

 us and constitute a variation which is evident to our senses. It is 

 exactly upon the intimate connection of direct physical action with 

 the consequences of natural selection that the strength of the Dar- 

 winian theory rests. 



The origin of varieties and races would appear, however, to consti- 

 tute only the first stage in the processes of the continual changes of 

 organisms. However slowly the process of selection may work, yet 

 there is no limit to the extent and magnitude of the changes, or to 

 the endless combinations of reciprocal adaptations of living beings if 

 we allow a very long period of time for its operation. With the 

 aid of this new factor of duration of time, which, according to geo- 

 logical facts, cannot be rejected, but stands to an unlimited extent at 

 our service, the gap between variety and species disappears. Since 

 the former are continually diverging with the lapse of time and the 

 more they do so and become differentiated in their organization so 

 much the better will they be fitted to fill different places in the eco- 

 nomy of nature and to increase in number they at length attain the 

 value of species, which in a state of nature do not interbreed, or, at 

 any rate, only exceptionally produce progeny. Thus, according to 

 Darwin, a variety is a species in process of formation. Variety and 

 species are connected by continuous series of transitions, and are not 

 absolutely distinct from one another ; but are only relatively separated 



