578 THE BEGINNINGS OF IIFE. 



representatives of a species — the ' natural selection ' of 

 some particular difference in these cases being deter- 

 mined by the advantage which fitness gives in the 

 ^ struggle for existence.' 



It is of course quite true that the first two causes 

 of variation, like the more minute and fortuitous in- 

 stances of variability, may be made use of as start- 

 ing-points for the further action of Natural Selection 

 where the struggle for existence is severe j and so far 

 Mr. Darwin's view would be thoroughly in accordance 

 with the facts. But it seems equally clear from the 

 vast amount of evidence, general and particular, which 

 Mr. Spencer has adduced^, that the direct and in- 

 direct influence of the conditions of life are really 

 independent producers of specific variability amongst 

 most of the forms of life outside the ephemeromorphic 

 world 2. So that they must stand side by side with 

 Natural Selection, if not as co-equals, yet as occu- 

 pying marked and important positions '^. The evidence 

 cited by Mr. Spencer concerning the direct influence of 

 external conditions is particularly strong in many of 



^ See ' Principles of Biology,' vol. i. p. 184, and vol. ii. 



^ Many of which are ' adaptive changes.' 



3 Mr. Darwin has lately, whilst admitting the possibility of his having 

 attached rather too exclusive an importance to the influence of Natural 

 Selection, asserted that his main objects in the ' Origin of Species ' were 

 ' firstly, to show that species had not been separately created; and, 

 secondly, that Natural Selection had been the chief agent of changes, 

 though largely aided by the inherited effects of habit, and slightly by 

 the direct action of the surrounding conditions.' (' Descent of Man,' 

 chap. iv. 1870.) 



