DARWINISM DEFENDED. 153 



Tayler, 1 ' making a general defence of the natural selection 



theory, says : "To realise how far the theory of selection is 



capable of explaining the facts of organic evo- 



eral defense of lution, it is necessary to bear in mind the 



natural selection, postu i ates on w hi c h the theory is founded. 



"i. It is obvious that natural selection can only act by 

 preserving or eliminating the complete organism. Selection 

 must therefore be organismal. This Darwin and other 

 selectionists have clearly recognised. 



"2. As the whole organism must survive, if the favoura- 

 ble variation or variations are to be preserved, it follows that 

 certain minor unfavourable variations may also be pre- 

 served if they happen to exist in an individual which sur- 

 vives on account of its major favourable variations. And 

 since no individual is completely adapted to its environment, 

 it follows that there must be always a variable amount of 

 residual unfavourable variability in every organism. 



"3. This residual unfavourable variability may be of con- 

 siderable utility under changed conditions. 



"4. Complementary specialisation of parts, as Spencer 

 has shown, is favourable to successful competition, and as it 

 is the whole organism that is selected or eliminated, it fol- 

 lows that any weakness of one specialised part, since it would 

 disturb the balance of all, would be detrimental. The more 

 complex the organism, the more specialised the structures, 

 the more dependent one part will be on the others for its 

 existence, hence a complementary specialising tendency will 

 be favoured by selection, and therefore all struggles of one 

 part of an organism with another will be reduced to a 

 minimum. 



"It is clear that there must be some underlying criterion 

 which determines whether any given organism shall be 

 selected or not, and that criterion must be the net result of 

 its adaptability to its environment. One organism may con- 

 ceivably survive, by its possession of a large number of small 



