146 DARWINISM TO-DAY. 



environment and therefore favourable to more complete 

 modification of the somatic side of the organism ; this tend- 

 ency being accumulative under constant conditions, coinci- 

 dent variability would arise by the process of selective 

 elimination and preservation, without the need of the 

 assumption of use-inheritance, which assumption facts 

 appear to negative. 



Against the criticism that natural selection cannot explain 



over-developments of specialisation, that is, the carrying 



unnecessarily far of advantageous structural 



objection 1 con- * an ^ functional development, as illustrated by 



cemingover- the great antlers of stags and moose, the micro- 

 specialisation, ! F ' 



scopic fidelity of simulation and mimicry, and 

 the nearly identical equivalence of the right and left halves 

 of bilaterally symmetrical animals, the selectionist has little 

 to offer except the always pertinent questions : Are we sure 

 that the case in point is one of over-development, of unnec- 

 essary specialisation? And although the palseo-zoologists 

 may be pretty emphatic in their declarations that the ex- 

 tinction of the Irish stag and of the unwieldy cretaceous 

 reptiles was directly due to over-specialisation, they cannot 

 prove it. And there you are, says the Darwinist. 



The difficulty that natural selection has with structural 

 degeneration is admittedly a real one. The strict Darwinian- 

 answer has to be that retrogression is produced 

 of the^bjection either by reversed selection, that is, that when 

 concerning de- by a change in the life habits or external condi- 



generation, . .... . . 



tions a certain function or organ becomes inju- 

 rious, as in the case of insects on small exposed islands 

 where the wind might carry the flying ones off into the 

 ocean, selection, on the basis of advantage, would tend to 

 preserve the ones most poorly equipped for flight; or it 

 has to be that when the function of an organ is, because of 

 change in habit or conditions, once neglected or discon- 

 tinued, that is, the organ is no longer used, any slight varia- 



