64 CREATIVE EVOLUTION [chap. 



It must not be forgotten that all the parts of an organism 

 are necessarily coordinated. Whether the function be 

 the effect of the organ or its cause, it matters little; one 

 point is certain — the organ will be of no use and will not 

 give selection a hold unless it functions. However the 

 minute structure of the retina may develop, and however 

 complicated it may become, such progress, instead of 

 favoring vision, will probably hinder it if the visual centres 

 do not develop at the same time, as well as several parts of 

 the visual organ itself. If the variations are accidental, 

 how can they ever agree to arise in every part of the organ 

 at the same time, in such way that the organ will con- 

 tinue to perform its function? Darwin quite understood 

 this; it is one of the reasons why he regarded variation 

 as insensible. 1 For a difference which arises accidentally 

 at one point of the visual apparatus, if it be very slight, 

 will not hinder the functioning of the organ; and hence 

 this first accidental variation can, in a sense, wait for comple- 

 mentary variations to accumulate and raise vision to a 

 higher degree of perfection. Granted; but while the 

 insensible variation does not hinder the functioning of 

 the eye, neither does it help it, so long as the variations 

 that are complementary do not occur. How, in that case, 

 can the variation be retained by natural selection? Un- 

 wittingly one will reason as if the slight variation were a 

 toothing stone set up by the organism and reserved for a 

 later construction. This hypothesis, so little conformable 

 to the Darwinian principle, is difficult enough to avoid 

 even in the case of an organ which has been developed along 

 one single main line of evolution, e.g. the vertebrate eye. 

 But it is absolutely forced upon us when we observe the 

 likeness of structure of the vertebrate eye and that of the 

 molluscs. How could the same small variations, incal- 



1 Darwin, Origin of Species, chap. vi. 



