232 THE PHILOSOPHY OF BIOLOGY 



individual. It is easy to see how co-ordination of 

 mutating parts is absolutely essential. An animal 

 which preserves its existence by successful avoidance 

 of its enemies would not be greatly benefited by a 

 more transparent crystalline lens if the vitreous humour 

 of its eye were slightly opaque ; and even if all the 

 parts of the eye were perfectly co-ordinated, increased 

 acuity of vision would not greatly help it if its limbs 

 were not able to respond all the more quickly to the 

 more acute sensation. Un-co-ordinated mutations 

 would therefore tend to become eliminated, while 

 co-ordinated ones would become selected and would 

 become the characters of new species. 



We must now ask why some groups of variations 

 are co-ordinated while others are not, and it is here 

 that we encounter the most formidable of the difficulties 

 of any hypothesis of transformism which depends on 

 the concept of natural selection. If we assume that 

 the environment induces the appearance of variations, 

 it seems to follow that these variations are likely to be 

 co-ordinated, but we then invoke the principle of the 

 acquirement of characters and their transmission by 

 heredity. If, on the other hand, we assume that varia- 

 tions appear spontaneously, and quite irresponsibly, 

 so to speak, in the germ-plasm of the organism, the 

 selection, or elimination, by the environment will not 

 occur until the co-ordinated or un-co-ordinated varia- 

 tions appear. It is far more likely that a large number 

 of simultaneously appearing variations will be un-co- 

 ordinated than that they will be co-ordinated. Merely 

 as a matter of probability the progressive modification 

 of a species will take place slowly — too slowly to account 

 for what we see. 



Two examples wall make it easier to appreciate this 

 difiiculty. Evolution has undoubtedly proceeded in 



